The Unix Hardware Buyer HOWTO

Eric Raymond


<esr@thyrsus.com>

Revision History                                                             
Revision 4.0           2007-11-02            Revised by: esr                 
Major revisions by Jonathan Marsden on SATA, bus standards, DVDs and other   
topics, followed by a cleanup pass from me.                                  
Revision 3.3           2007-18-13            Revised by: esr                 
Updated for 2007 conditions. CRTs are dead. BTX is dead. CD-ROMs are         
competely generic now. USB modems are recommended.                           
Revision 3.2           2004-10-28            Revised by: esr                 
Fix and remove bad links.                                                    
Revision 3.1           2004-08-03            Revised by: esr                 
Sound cards don't matter any more.                                           
Revision 3.0           2004-02-21            Revised by: esr                 
Power-protection stuff moved to UPS HOWTO. DIMM memory is gone. Tape drives  
don't make sense any more. Lots of the theory from my "Ultimate Linux Box"   
articles now lives here.                                                     
Revision 2.4           2003-02-22            Revised by: esr                 
URL fixes.                                                                   
Revision 2.3           2002-08-06            Revised by: esr                 
Buying at the low end isn't a lose anymore. I recommend Athlons. Nuked the   
section on video standards, EDID takes care of all that now. Also removed the
section on older memory types. And keyboards, as the "ergonomic" ones all    
vanished along with the 1990s carpal-tunnel scare.                           
Revision 2.2           2002-08-05            Revised by: esr                 
New section on DVD drives.                                                   
Revision 2.1           2002-07-08            Revised by: esr                 
Corrected Kingston URL. Various small updates for the last year. This HOWTO  
is much more stable than it used to be.                                      
Revision 2.0           2001-08-09            Revised by: esr                 
Major update. Revisions based on Ultimate Linux Box experience. Caches are   
on-chip now. DDS4 tape drives are here. 486 machines, CD caddies, and most   
non-DDS backup technologies are gone.                                        
Revision 1.1           2001-06-13            Revised by: esr                 
Mid-2001 update.                                                             
Revision 1.0           2001-02-06            Revised by: esr                 
Initial revision; but see the history in the introduction.                   


 This is your one-stop resource for information about how to buy and
configure generic PC hardware for cheap, powerful Unix systems.

-----------------------------------------------------------------------------
Table of Contents
1. Introduction
    1.1. Purpose of this document
    1.2. New versions of this document
    1.3. Feedback and corrections
    1.4. Related resources
   
   
2. Overview of the Market
3. Buying the Basics
    3.1. Things to Not Care About
    3.2. How To Pick Your Processor
    3.3. One Disk or Two?
    3.4. Getting Down to Cases
    3.5. Power Supplies and Fans
    3.6. Motherboards
    3.7. Monitor and Video
    3.8. DVD Drives
    3.9. Sound Cards and Speakers
    3.10. Modems
    3.11. Printers
    3.12. Power Protection
    3.13. Radio Frequency Interference
   
   
4. What To Optimize
    4.1. First, add more memory
    4.2. Bus and Disk speeds
    4.3. Disk Wars: SATA vs. SCSI
    4.4. Tuning Your I/O Subsystem
   
   
5. But What If I'm Economizing?
6. Noise Control and Heat Dissipation
7. Special Considerations When Buying Laptops
8. How to Buy
    8.1. When to Buy
    8.2. Where to Buy
    8.3. Computer Fairs
    8.4. Mail Order
    8.5. Computer Superstores
    8.6. Other Buying Tips
   
   
9. Questions You Should Always Ask Your Vendor
    9.1. Minimum Warranty Provisions
    9.2. Documentation
    9.3. A System Quality Checklist
   
   
10. Things to Check when Buying
    10.1. Tricks and Traps in Warranties
    10.2. Special Questions to Ask Web/Mail-Order Vendors Before Buying
    10.3. Payment Method
    10.4. Which Clone Vendors to Talk To
   
   
11. After You Take Delivery
12. Software to go with your hardware
13. Other Resources on Building Linux PCs

1. Introduction

1.1. Purpose of this document

The purpose of this document is to give you the background information you
need to be a savvy buyer of Intel hardware for running Unix. It is aimed
especially at hackers and others with the technical skills and confidence to
go to the Internet/mail-order channel, but contains plenty of useful advice
for people buying store-front retail.

This document is maintained and periodically updated as a service to the net
by Eric S. Raymond, who began it for the very best self-interested reason
that he was in the market and didn't believe in plonking down several grand
without doing his homework first (no, I don't get paid for this, though I
have had a bunch of free software and hardware dumped on me as a result of
it!). Corrections, updates, and all pertinent information are welcomed at
[mailto:esr@snark.thyrsus.com] esr@snark.thyrsus.com. The editorial we??
reflects the generous contributions of many savvy Internetters.

If you email me questions that address gaps in the FAQ material, you will
probably get a reply that says "Sorry, everything I know about this topic is
in the HOWTO". If you find out the answer to such a question, please share it
with me for the HOWTO, so everyone can benefit.

If you end up buying something based on information from this HOWTO, please
do yourself and the net a favor; make a point of telling the vendor "The
HOWTO sent me" or some equivalent. If we can show vendors that this HOWTO
influences a lot of purchasing decisions, we get leverage to change some
things that need changing.

Note that in December 1996 I published an introductory article on building
and tuning Linux systems summarizing much of the material in this HOWTO. It's
available here. In 2001 I published an article on building the Ultimate Linux
Box.

This Buyer's Guide actually dates back to 1992, when it was known as the 
"PC-Clone Unix Hardware Buyer's Guide"; this was before Linux took over my
world :-). Before that, portions of it were part of a Unix Buyer's Guide that
I maintained back in the 1980s on USENET.

It may be a matter of historical interest that the page count of this guide
peaked in mid-2001 and has been declining since. Video, sound, and other
functions are migrating onto motherboards. Several bus types have
disappeared, as have all the old-school backup technologies that couldn't
scale up to match disk capacities, Spec sheets are getting simpler.
Accordingly, there are parts that used to have whole sections to hemselves
that I barely even write about anymore ?? mice, floppy disks, CD-ROM drives,
and keyboards, for example, are utterly generic now,

Another consequence of the technology stabilizing is also that I'm updating
this guide less often than I used to. Years can now go by without the PC
market changing in any fundamental way.

In retrospect, the success of the ATX standard for motherboards in 1998-1999
was probably the turning point. The PC industry has become sufficiently
commoditized that your choices are now getting simpler rather than more
complicated. This is a Good Thing.
-----------------------------------------------------------------------------

1.2. New versions of this document

New versions of the Unix Hardware Buyer HOWTO will be periodically be
uploaded to various Linux WWW and FTP sites, including the LDP home page.

You can view the latest version of this on the World Wide Web via the URL
[http://www.tldp.org/HOWTO/Unix-Hardware-Buyer-HOWTO/] http://www.tldp.org/
HOWTO/Unix-Hardware-Buyer-HOWTO/.
-----------------------------------------------------------------------------

1.3. Feedback and corrections

If you have questions or comments about this document, please feel free to
mail Eric S. Raymond, at [mailto:esr@thyrsus.com] esr@thyrsus.com. I welcome
any suggestions or criticisms. If you find a mistake with this document,
please let me know so I can correct it in the next version. Thanks.
-----------------------------------------------------------------------------

1.4. Related resources

You may also want to look at the read the [http://www.tldp.org/HOWTO/
Hardware-HOWTO.html] Hardware-HOWTO. It lists hardware known to be compatible
with Linux, and hardware known to be incompatible. I've also done a series of
articles on The Ultimate Linux Box.
-----------------------------------------------------------------------------

2. Overview of the Market

The central fact about PC hardware is that de-facto hardware standards have
created a commodity market with low entry barriers, lots of competitive
pressure, and volume high enough to amortize a lot of development on the
cheap.

The result is that this hardware gives you lots of bang-per-buck, and it's
getting both cheaper and better all the time. Furthermore, margins are thin
enough that vendors have to be lean, hungry, and very responsive to the
market to survive.

One good general piece of advice is that you should avoid the highest-end
new-technology systems (those not yet shipping in volume). The problem with
the high end is that it usually carries a hefty "prestige" price premium, and
may be a bit less reliable on average because the technology hasn't been
through a lot of test/improve cycles.

There used to be a real issue with low-end PCs as well, because there used to
be a lot of dodgy crap PC components out there going into boxes made by
vendors trying to save a few cents. That's not really a problem anymore.
Market pressure has been very effective at raising reliability standards for
even low-end components as the market has matured. It's actually hard to go
wrong even buying at the bottom end of the market these days.

I put together the first version of this guide around 1992; Unix-capable
systems are now ten to twenty times cheaper than they were then. At today's
prices, building your own system from parts no longer makes much sense at all
??so this HOWTO is now more oriented towards helping you configure a whole
system from a single vendor.
-----------------------------------------------------------------------------

3. Buying the Basics

In this section, we cover things to look out for that are more or less
independent of price-performance tradeoffs, part of your minimum system for
running Unix.

Issues like your choice of disk, processor, and I/O bus (where there is a
significant tradeoff between price and capability) are covered in the section
on What To Optimize.
-----------------------------------------------------------------------------

3.1. Things to Not Care About

An effect of PC commoditization is that there aren lots of things you used to
have to worry about that don't matter any more, because the market has
completely flattened out. We list these here to get them out of the way.
-----------------------------------------------------------------------------

3.1.1. Bus Wars

The system bus is what ties all the parts of your machine together. This is
an area in which progress has simplified your choices a lot. There used to be
no fewer than four competing bus standards out there (ISA, EISA, VESA/VLB,
PCI, and PCMCIA). Now there are effectively just two ??PCI-X on servers, and
PCIe for desktop/tower machines. Even PCI is now legacy technology, and the
PCMCIA bus that seemed so important a few years back has been reduced to
near-irrelevance by Ethernet and WiFi hardware built onto motherboards. The
newcomer is PCIe, which is (in late 2007) a ??video-card-mostly?? bus, though
it seems to be gaining in popularity for other uses too on mainstream desktop
motherboards, whereas PCI-X is only found on higher end ??server??
motherboards.
-----------------------------------------------------------------------------

3.1.2. Memory

Judging the memory-controller and cache design used to be one of the
trickiest parts of evaluating a motherboard, but that stuff is all baked into
the processor itself now. This removed a large source of latency and design
variations. It also killed off the plethora of different RAM types that used
to be out there.

Today's advice is very simple. Make sure the memory is rated for your
machine's bus speed, then buy as much as you can afford to stuff in your
machine.

Note DDR3 RAM is beginning to appear. Right now its extra expense over DDR2  
     is not worth paying, for all but extremely specialized needs. It is     
     almost always far more useful to have 4GB of reasonably fast RAM, than  
     2GB of very fast RAM, in your machine.                                  

For more technical stuff on memory architectures, see The Ultimate Memory
Guide maintained by Kingston Technologies.
-----------------------------------------------------------------------------

3.1.3. Keyboards and Mice

Keyboards are mostly generic nowadays. One useful piece of advice is to not
buy any desktop machine with "Internet" buttons on it; this is a sure sign of
a PC that's an overpriced glitzy toy. Nowadays keyboards with a USB connector
are the norm, rather than the older dedicated connectors; modern open-source
Unixes handle these just fine.

Mice and trackballs used to be simple; then, thanks to Microsoft, they got
complicated. Now they're simple again. Again, USB mice have replaced the
older PS/2-style dedicated connector. XFree86 autodetects your mouse when it
starts up, so configuration is not a big deal any more.

Some PC vendors, being Windows-oriented, still bundle two-button mice. Thus,
you may have to buy your own three-button (or two button and a scroll wheel)
mouse. Ignore the adspeak about dpi and pick a mouse or trackball that feels
good to your hand.

Your humble editor really, really likes the Logitech TrackMarble, an optical
trackball that eliminates the chronic roller-fouling problems of the older
TrackMan. They're well-supported by X, so any Linux or BSD will accept them.
-----------------------------------------------------------------------------

3.1.4. Floppy Drives

There's no longer much to be said about floppy drives. They're cheap, they're
generic, and the rise of CD-ROM and DVD-ROM drives as a cheap distribution
medium has made them much less important than formerly. You only ever see the
3.5-inch ??hard-shell?? floppies with 1.44MB capacity anymore.

Bootable CD-ROMs killed off the last use of floppies, which was OS
installation. So go ahead and settle for cheap Mitsumi and Teac floppy
drives. There are no ??premium?? floppy drives anymore. Nobody bothers.

It's possible your system won't even include one. No loss.
-----------------------------------------------------------------------------

3.1.5. CD-ROM Drives

Standard CD-ROMs hold about 650 megabytes of read-only data in a format
called ISO-9660 (formerly "High Sierra"). All current Unixes support these
devices. Unix and Linux software is now distributed on ISO-9660 CD-ROM, a
cheaper and better method than the QIC tapes we used to use.

CD-ROM speed used to be a big deal; vendors advertised 2X, 4X, all the way up
to 52X. Vendors don't bother any more; the drives are all about equivalently
fast now.

There are one or two minor features to watch for. Most CD-ROMS will include a
headphone jack so you can play audio CDs on them. Better-quality ones will
also include two RCA jacks for use with speakers. Another feature to look for
is a drive door or seal that protects the drive head from dust.

Increasingly, DVD-ROM drives (and burners) are replacing CD-ROM drives as the
default optical drive in PC systems. They have significantly larger capacity,
and will read (and burn) CD media too. The cost difference now is so small
that it is usually preferable to buy a DVD burner instead of a CD-ROM drive.
-----------------------------------------------------------------------------

3.1.6. Backup devices

It's good to be able to make backups that you can separate from your system
and store off-site in case of disaster. Until about 2001, tape drives still
seemed like a good idea for personal systems, but I found I seldom used mine.
Today, tape drive with high enough capacity to image today's huge hard disks
are too expensive to make sense any more.

For the money you'd spend on a high-capacity tape drive (over $1000) it makes
more sense to buy a laptop and a pile of CD-R or DVD-R or DVD+R media. Sit
the laptop on your house Ethernet when you're not traveling, and back up the
main machine to it every day, or oftener. Between the efficiency of rsync and
the speed of 100-megabit Ethernet, this will be a lot faster than making a
tape. Every once in a while, burn a set of backup CD-ROMs or DVDROMs.

But CD-ROMs aren't reusable; the cost piles up over time. An interesting
alternative is a small external USB hard drive, especially if you can salvage
an old laptop drive and put it in a USB enclosure. These enclosures are
available for about $30; Google for "USB HD Enclosure". This is faster than a
tape, cheaper and lighter than a full laptop. For faster transfer speeds, an
enclosure that accepts eSATA connections as well as USB helps a lot (assuming
your PC or notebook has an eSATA connector).
-----------------------------------------------------------------------------

3.2. How To Pick Your Processor

Right now (late 2007), the chips to consider for running Unix are the the
64-bit AMD Opteron or its Intel equivalents. We've basically passed the point
at which 32-bit chips are interesting for new desktop systems; choosing one
won't save you more than small change any more. The transition isn't complete
in laptops yet, which are mostly still using 32-bit chips to minimize their
power draw.

Brands don't matter much, so don't feel you need to pay Intel's premiums if
you see an attractive Cyrix, AMD or other chip-clone system offered. In the
last few years I've become a big fan of the AMD line. They used to be faster,
cheaper, and better-designed than Intel processors; today Intel has clawed
back the speed advantage, but AMD chips still deliver more performance than
you're likely to be able to use and do it with lower power dissipation (thus,
less noise and heat).

Many CPUs now are multi-core ?? that is, they have multiple CPUs on a single
chip. This is very useful for doing something compute intensive (re-encoding
video, compressing large archives, etc.) in the background and still having a
responsive system for other work at the same time. At current prices, a
dual-core CPU makes good sense for most desktop systems. If you are creating
a server or have specialized computing needs you expect to be very
CPU-intensive, quad-core is worth considering. Only at the very low end (sub
US$50 CPUs) do single-core CPUs still make sense on desktop machines.

Mainstream desktop CPUs now use one of two sockets: LGA 775 (Intel) and AM2
(AMD). Buying a system that uses one of these stands more chance of allowing
a useful CPU upgrade to extend its useful life than systems using other less
common sockets.

Current CPUs are much faster than those of just a few years ago. As a result,
unless your needs are highly specialized, spending more than about US$200 on
a desktop CPU is hard to justify. Putting extra budget into more RAM or a
faster disk subsystem will most likely result in greater benefit to most
users.
-----------------------------------------------------------------------------

3.3. One Disk or Two?

I usually build with two disks ?? one "system" disk and one "home" disk.
There are two good reasons to do this that have nothing to do with the extra
capacity. One of them is the performance advantage of being able to
interleave commands to different physical spindles that we'll explain a bit
later in the section on disks. The other is that I am quite a bit less likely
to lose two disks at once than I am to trash a single one.

Let's suppose you have a fatal disk crash. If you have only one disk, goodbye
Charlie. If you have two, maybe the crashed one was your system disk, in
which case you can buy another and mess around with a new Linux installation
knowing your personal files are safe. Or maybe it was your home disk; in that
case, you can still run and do recovery stuff and basic Net communications
until you can buy another home disk and restore it from backups (you did keep
backups, right?).

Given today's high capacity drives, another way to use two disks well is to
set them up as a RAID1 (mirrored) array. This can be done in software or with
a hardware RAID controller. This way if either of the two drives fail, the
system will continue to function, no data is lost, and upon replacing the
failed drive, the array can be rebuilt from the remaining working drive. Hard
drives are consumable media, they do fail, so this approach (as well as good
backups) is well worth considering.

Your performance-tuning choice is SATA versus SCSI (the older IDE and EIDE
buses are now obsolete). We'll have more to say about that in Section 4.
-----------------------------------------------------------------------------

3.4. Getting Down to Cases

I used to say that cases are just bent metal, and that it doesn't much matter
who makes those. Unfortunately, this isn't true any more. Processors run so
hot these days that fans and airflow are a serious concern. They need to be
well designed for proper airflow throughout.

Look for the following quality features:

*Aluminum rather than steel. It's lighter and conducts heat better.
   
*Unobstructed air intake with at least one fan each (in addition to the
    power supply and processor fans)
   
*No sharp metal edges. You don't want to shred your hands when you're
    tinkering with things.
   
*There shouldn't be any hot spots (poor air flow).
   
*Sturdy card clips. Some poorly-designed cases allow cards to wiggle out
    of their slots under normal vibration.
   
*Effective and easy to use mechanisms for attaching hard drives, CD-ROM,
    CD-R/W, DVDs, etc.
   

If you're fussy about RFI (Radio-Frequency Interference), it's worth finding
out whether the plastic parts of the case have conductive coating on the
inside; that will cut down emissions significantly, but a few cheap cases
omit it.

Should you buy a desktop or tower case? Our advice is go with tower unless
you're building a no-expansions personal system and expect to be using the
floppies a lot. Many vendors charge nothing extra for a tower case, and the
cost difference will be trivial even if they do. What you get for that is
less desktop clutter, more and bigger bays for expansion, and often (perhaps
most importantly) a beefed-up power-supply and fan. Putting the box and its
fan under a table is good for maybe 5db off the effective noise level, too.
Airflow is also an issue; if the peripheral bays are less cramped, you get
better cooling. Be prepared to buy extension cables for your keyboard and
monitor, though; vendors almost never include enough flex.

The airflow thing is a good argument for a full- or mid-tower rather than the
??baby tower?? cases some vendors offer. However, smaller towers are getting
more attractive as boards and devices shrink and more functions migrate onto
the motherboard. A state of the art system, with all 3" disks, 300W power
supply, half-size motherboard, on-board SATA and 4GB of RAM sockets, and
half-sized expansion cards, will fit into a baby or midsized tower with ample
room for expansion; and the whole thing will fit under a desk and make less
noise than a classic tower.

For users with really heavy expansibility requirements, rackmount PC cases do
exist (ask prospective vendors). Typically a rackmount case will have pretty
much the same functionality as an ordinary PC case. But, you can then buy
drive racks (complete with power supply), etc. to expand into. Also, you can
buy passive backplanes with up to 20 or so slots. You can either put a CPU
card in one of the slots, or connect it to an ordinary motherboard through
one of the slots.
-----------------------------------------------------------------------------

3.5. Power Supplies and Fans

A lot of people treat power supplies as a commodity, so many interchangeable
silver bricks. We know better ?? cheap power supplies go bad, and when they
go bad they have a nasty habit of taking out the delicate electronics they're
feeding. Also, the power supply tends to be the noisiest component in your
system.

Give preference to supplies with a Underwriter's Laboratories rating. There's
some controversy over optimum wattage level. On the one hand, you want enough
wattage for expansion. On the other, big supplies are noisier, and if you
draw too little current for the rating the delivered voltage can become
unstable. And the expected wattage load from peripherals is dropping
steadily. On the other hand, processors and their cooling fans eat a lot more
power than they used to.

The choice is generally between 200W and 300W. After some years of
deprecating 300W-and-up supplies as overkill, I'm now persuaded it's time to
go back to them; a modern processor can consume 50-75W by itself, and for the
newer dual-processor board the power supply needs to be rated 450W or up.

Processors on modern motherboards run hot enough that all vendors have gone
to embedded temperature sensors and variable-speed thermostat-controlled
fans, out sheer self-defense (this used to be a high-end only feature).

To cut noise, look for 120mm fans rather than the old-style 80mm muffin fans.
These can move the same amount of air per minute rotating at a lower tip
speed, which means less vortex formation and less noise. These are now
becoming standard even on cheap white-box hardware.

In garden-variety tower cases there often isn't enough airflow to cool all
components effectively with a single fan, even going at full speed. And the
single fan in the power supply was basically designed to cool the power
supply, not the components in the case. This is why processors and some
graphics cards have their own fans now.

A few years ago PCs often had two or more case fans in addition to the
power-supply fan. This made sense in the era of 80mm fans and lots of
expansion cards obstructing the airflow, but it was noisy. Nowadays, with
sound and graphics and Ethernet integrated onto motherboards, expansion cards
are much less common (and processors carry their own mini-fans). Thus,
today's standard is to mount one 120mm fan, usually low and forward just
beneath the disk-drive stack. This is much quieter, like by a factor of three
or four.

The noise produced by a fan is not just a function of the speed with which it
turns. It also depends on the nature of the airflow produced by the fan
blades and the bearings of the rotor. If the blades cause lots of turbulent
airflow, the fan produces lots of noise. One brand of fans that is much more
silent than most others even if going at full throttle is [http://
www.papstplc.com/] Papst.
-----------------------------------------------------------------------------

3.6. Motherboards

Provided you exercise a little prudence and stay out of the price basement,
motherboards and BIOS chips don't vary much in quality. There are only six or
so major brands of motherboard inside all those cases and they're pretty much
interchangeable; brand premiums are low to nonexistent and cost is strictly
tied to maximum speed and bus type. There are only four major brands of BIOS
chip (AMI, Phoenix, Mylex, Award) and not much to choose between 'em but the
look of the self-test screens (even the "name" vendors use lightly customized
versions of these). One advantage Unix buyers have is that Unixes are built
not to rely on the BIOS code (because it can't be used in protected mode
without more pain than than it's worth). If your BIOS will boot properly,
you're usually going to be OK.

Some good features to look for in a motherboard include:

*Gold-plated contacts in the expansion slots and RAM sockets. Base-metal
    contacts tend to grow an oxidation layer which can cause intermittent
    connection faults that look like bad RAM chips or boards. (This is why,
    if your hardware starts flaking out, one of the first things to do is
    jiggle or remove the boards and reseat them, and press down on the RAM
    chips to reseat them as well ??this may break up the oxidation layer. If
    this doesn't work, rubbing what contacts you can reach with a soft eraser
    is a good fast way to remove the oxidation film. Beware, some hard
    erasers, including many pencil erasers, can strip off the plating, too!)
   
*The board should be speed-rated as high as your processor, of course.
    It's good if it's rated higher, so upgrade to a faster processor is just
    a matter of dropping in the chip and a new crystal.
   

(I used to have "Voltage, temperature and fan speed monitoring hardware." on
this list. But processors run so hot nowadays that all current motherboards
have it.)

The dominant form factor is still ATX. Intel tried to replace it with a new
standard called BTX in late 2004-2005, but failed; the proposal was
effectively withdrawn in 2006. In January 2007 AMD announced a [http://
www.dtxpc.org/] DTX specification for small-form-factor PCs; it remains to be
seen whether this will gain any traction.
-----------------------------------------------------------------------------

3.7. Monitor and Video

The largest user-visible change since the last major update of this guide is
that the CRT (cathode-ray tube) is dead. The manufacturers shut down their
production lines in late 2004; the remaining CRTs out there are old stock
that's been sitting in warehouses. The only reason to buy one since then has
been to get high-end resolution at a price lower than the insanely expensive
high-end flatscreens; with 1920x1440 flatscreens now (late 2007) becoming
generally available at reasonable prives even that reason is gone. It's all
flatscreens now, baby.

On flatscreens, only two statistics matter; pixel size and response time. The
biggest functional drawback of flatscreens relative to CRTs is that they
refresh more slowly, because cheical reactions in a flatscreen pixel take
longer than remodulating a flying electron beam. You'll never notice this
during ordinary desktop use, but it can cause streakiness and artifacts when
you're playing games or viewing movies. If you're going to do that a lot, the
price premium for a flatscreen with better response time may be worth it.

Next, buy your card (if you have to; see next paragraph). This used to be
complicated, with issues like matching the video bandwidths of the card and
the CRT, and the amount of display memory. Now (unless you are a gamer or
have similarly extreme 3D acceleration requirements) it's simple; all cards
have enough display memory for every resolution in use, and the issues are
software (does it have an open-source driver, and do you care?)

It's actually fairly likely you'll never buy a video card again. Very capable
graphics chips are routinely integrated onto motherboards now; unless you're
a gamer or somebody else who absolutely must have the latest wheeze in 3D
acceleration, they'll be good enough. Even this is not a stable situation, as
3D acceleration is commoditizing too.

I used to carry a lot of material on different video standards, interlacing,
and flicker. That stuff is all obsolete now.

Here's what to look for on the monitor spec sheet:

*Screen size and format. Usually measured in diagonal inches. Many screens
    are now in a "widescreen" format (16:10 ratio of width:height) rather
    than the older 5:4 or 4:3 ratios common for CRTs and older flat panel
    screens. A "19 inch" widescreen monitor generally has considerably fewer
    pixels than a "19 inch" 5:4 ratio one.
   
*Screen resolution. 1280x1024 is now low end on the desktop. Seventeen
    inch 1280x1024 screens are the bargain basement now, some manufacturers
    already switching production to 19 inch widescreen 1440x900 screens
    instead. In late 2007, the cost difference between such screens and 20
    inch 1680x1050 screens is very small, making the 20 inch screens a better
    choice unless funds (or desktop space!) are very tight.
   
*5ms or lower response time. 3ms is better. There is some marketing-speak
    going on in the way the response time is specified (grey to gray rather
    than black to white) but since most manufacturers do it this way these
    times are usually comparable between different manufacturers screens.
   
*Does it have a tilt-and-swivel base? Adequate controls, including both
    horizontal and vertical size and horizontal and vertical centering? A
    color-temperature control is a plus; the last is particularly important
    if you compose graphics on screen for hardcopy from a printer.
   

If you can, buy your monitor from someplace that will let you see the same
monitor (the very unit you will walk out the door with, not a different or
`demo' unit of the same model) that will be on your system. There's
significant quality variation (even in "premium" monitor brands) even among
monitors of the same make and model.
-----------------------------------------------------------------------------

3.8. DVD Drives

DVD drives have two main uses in computer systems: playback of video DVDs,
and use for data storage (either installation media or backups, or even as a
primary drive in a few specialized systems).
-----------------------------------------------------------------------------

3.8.1. DVDs for Data Storage

DVD burners (drives that can read and write CDROM media as well as several
kinds of DVD media) are now low cost and useful. Most come with either a
parallel ATA ("IDE") interface or, increasingly, a SATA interface. Linux and
most current PC Unix-like systems will work fine with either interface. Given
the choice, SATA is slightly preferable because the cable is smaller and
simpler, and modern motherboards have more SATA connections than parallel ATA
ones.

There is probably little or no benefit in seeking out a DVD drive with a SCSI
interface any longer.
-----------------------------------------------------------------------------

3.8.2. DVDs for Video Playback

(Most of this section courtesy of James Turinsky.)

If you only need to watch video DVDs sold for and intended to be played in
your own "region" of the world, you may skip this section.

Most drives manufactured after January 1st 2000, and some drives prior to
that have come installed with something called RPC2.

When a drive is RPC2, it means that it stores the Region code physically
within the drive. This means that nothing you do on the software level will
be of any help (including using DVD Genie or formatting your hard drive).

The only means of bypassing this Regional Protection Scheme is by using a
firmware patch. A firmware patch is a special piece of software written for a
specific DVD Drive model. It will only works on that specific model.

The original role of the firmware patch was to fix minor flaws in the drive
logic (a piece of programmable software within the drive, also referred to as
a "Firmware"). This logic also controls the Region Checks, so some inventive
programmers have modified these firmware patches to remove the portion of
logic that does the Regional checks, thus making the drive region-free (RPC1
stands for region free).

However, since a firmware patch is specific to one drive model, it's
impossible to make a global fix for all drives on the hardware level. This
limitation requires programmers to modify each firmware patch that comes out
for various drives. And here lies the problem. Modifying a firmware is not a
simple task, it requires good understanding of the hardware and some advanced
programming skills. To top this off, there are quite a few DVD Drive models
out there, and not as many programmers with the skill that can access these
drives. So in reality, not all drives have firmware patches that can make the
drive region free.

So some foresight is required when buying a new DVD drive. You should check
if someone already released a patched firmware for the model you wish to buy.

For more, see the Firmware Patches site.
-----------------------------------------------------------------------------

3.9. Sound Cards and Speakers

You can't buy a really bad sound card any more. Even low-end sound cards or
the sound chips embedded in a lot of PC motherboards these days support
support all these features:

*16-bit sampling (for 65536 dynamic levels rather than 256).
   
*Mono and stereo support.
   
*Full-duplex mode.
   
*Sampling rate of 44.1KHz (CD-quality).
   
*MIDI interface via a standard 15-pin D-shell connector.
   
*RCA output jacks for headphones or speakers.
   
*A microphone jack for sound input.
   

If you are interested in multi-track digital recording, two particularly good
choices are the M-Audio Delta, or RME Hammerfall series of cards. Decent (and
lower cost!) two-channel cards for more normal use are those using the
ICE1712 (Envy24) and ICE1724 (Envy24HT) audio chips. For normal users,
though, almost anything will work fine!

A rather comprehensive list of sound cards and chips supported by the ALSA
project, which is the main way sound cards are supported under Linux, can be
found at ALSA Sound Card Matrix.

In speakers, look for a magnetically-shielded enclosure with volume, bass and
treble controls. Some speakers run off the card's 4-watt signal; others are 
"self-powered", using batteries or a separate power supply. Your major buying
choice is which one of these options to pursue. Usually you'll want
separately-powered speakers. If appropriate for your listening habits, a pair
of decent headphones will get you better quality sound for the money compared
to speakers.

One final, important tip: that audio cable from your CD-ROM back to the sound
card is used only when you play audio CD-ROMs through your speakers.
Software-generated sound goes through the system bus, so you can play games
with sound even if your sound board won't accept the audio cable connector.
-----------------------------------------------------------------------------

3.10. Modems

Demand for (dialup telephone) modems is dropping as more and more people get
broadband Internet through DSL and cable. This section still has as much
detail as it does only because (a) there are people out beyond the exurbs who
can't get broadband, and (b) there are one or two remaining traps for the
unwary.

The modem market has stabilized and standardized. If you can spend $59, get a
U.S. Robotics V.92 USB external. You can then know that you've got the best
and skip the rest of this section. If you really must economize, spend $39
for the internal-card version (but you'll probably regret the $20 first time
you have to do diagnostics).

Note If you live somewhere with really bad telephone lines, the U.S. Robotics
     V.92 Business Modem may be truly "the best" for your needs, though it is
     about four times the price of the U.S. Robotics V.92 USB external, which
     is marketed for home use. See the [http://www.usrobotics.com] U.S.      
     Robotics web site for current product numbers and more detailed         
     specifications.                                                         

The modem market is like consumer electronics (and unlike the computer market
as a whole) in that price is a very poor predictor of performance. For
ordinary file transfers, some $50 modems are better than some $150 modems.
Paying top dollar mainly buys you better tolerance of poor connections and
better performance at heavy-duty bi-directional transfers (such as you would
generate, for exmaple, using SLIP or PPP over a leased line to an Internet
provider).

In today's market all modems do a nominal 56kbps ??V.90 and V.92 plus V.29 or
V.17 fax transmission and reception (over plain old phone lines you won't get
more than 53K of that). You don't see much in the way of slow/cheap to fast/
expensive product ranges within a single brand, because competition is fierce
and for many modem board designs (those featuring DSP (Digital Signal
Processor) chips run by a program in ROM) adding a new protocol is basically
a software change.
-----------------------------------------------------------------------------

3.10.1. Internal vs. External

Most modems come in two packagings: internal, designed to fit in a PC card
slot, and external, with its own case, power supply, and front-panel lights.
Typically you'll pay $20 to $30 more for an external modem than you will for
the internal equivalent. You'll also need a serial or USB port to connect
your external modem to.

Pay that premium ?? being able to see the blinkenlights on the external ones
will help you understand and recover from pathological situations. For
example, if your Unix system is prone to "screaming-tty" syndrome, you'll
quickly learn to recognize the pattern of flickers that goes with it. Punch
the hangup/reset button on an external modem and you're done ?? whereas with
an internal modem, you have to go root and flounder around killing processes
and maybe cold-boot the machine just to reset the card.

See Rick's Rants for extended discussion of this point.
-----------------------------------------------------------------------------

3.10.2. Pitfalls to Avoid

Don't buy a serial (RS232C) modem. This used to be the only kind there was,
but they were always a bitch to configure and troubleshoot. Go USB instead;
the sanity you save may be your own.

If the abbreviation "RPI" occurs anywhere on the box, don't even consider
buying the modem. RPI (Rockwell Protocol Interface) is a proprietary 
"standard" that allows modem makers to save a few bucks at your expense by
using a cheap-jack Rockwell chipset that doesn't do error correction.
Instead, it hands the job off to a modem driver which (on a Unix machine) you
will not have.

Also avoid anything called a "Windows Modem" or "WinModem", "HCF", or "HSP";
these lobotomized pieces of crap require a Windows DLL to run. They will eat
up to 25% of your processor clocks during transfers, and hog high-priority
interrupts (causing your machine to stall under Windows even if your
processor still has spare cycles).
-----------------------------------------------------------------------------

3.10.3. Fax Modems

Many modems come with bundled Windows fax software that is at best useless
under Unix, and at worst a software kluge to cover inadequate hardware. Avoid
these bundles and buy a bare modem ?? it's cheaper, and lowers the likelihood
that something vital to your communications needs has been left out of the
hardware.

Avoid "Class 1" and "Class 2" modems. Look for "Class 2.0" for the full
EIA-standard command set.

Fax capability is included with effectively all modems these days; it's cheap
for manufacturers, being basically a pure software add-on. The CCITT also
sets fax protocol standards. Terms to know:

V.29
    CCITT standard for Group III fax encoding at 9600bps
   
V.17
    CCITT standard for Group III fax encoding at 14400bps
   

There's a separate series of standards for software control of fax modems
over the serial (or USB) line maintained by the Electronics Industry
Association and friends. These are:

Class 1 ?? base EIA standard for fax control as extensions to the Hayes AT
command set.

Class 2.0 ?? enhanced EIA standard including compression, error correction,
station ID and other features.

Class 2 ?? marketroidian for anything between Class 1 and Class 2.0.
Different "Class 2" modems implement different draft subsets of the 2.0
standard, so "Class 2" fax software won't necessarily drive any given "Class
2" modem.

There's also a proprietary Intel "standard" called CAS, Communicating
Applications Specification. Ignore it; only Intel products support it.
-----------------------------------------------------------------------------

3.11. Printers

There really isn't all that much to be said about printers; the market is
thoroughly commoditized and printer capabilities pretty much independent of
the rest of your hardware. The PC-clone magazines will tell you what you need
to know about print quality, speed, features, etc. The business users they
feed on are obsessed with all these things.

(There used to be a problem with "GDI printers" and "WinPrinters" that only
worked with Windows ??they required special drivers that took over your CPU
to do image processing, These were such a bad idea that they have basically
disappeared off the market.)

Most popular printers are supported by GhostScript, and so it's easy to make
them do PostScript. If you're buying any letter-quality printer (laser or
ink-jet), check to see if it's on GhostScript's supported device list ??
otherwise you'll have to pay a premium for Postscript capability! Postscript
is still high-end in the Windows market, but it's ubiquitous in the Unix
world.

Warning, however: if you're using ghostscript on a non-Postscript printer,
printspeed will be slow, especially with a serial printer. A bitmapped 600
dpi page has a lot of pixels on it. At today's prices, paying the small
premium for Postscript capability makes sense.

If you're buying a printer for home, an inkjet is a good choice because it
doesn't use gobs of power and you won't have the toner/ozone/noise/etc mess
that you do with a laser. If all you want is plain-ASCII, dot-matrix is
cheaper to buy and run ?? if you can find one. Inexpensive ink-jets and
lasers have almost driven them off the market.

Inkjets are great in that they're cheap, many of them do color, and there are
many kinds which aren't PCL but are understood by Ghostscript anyway. If you
print very infrequently (less than weekly, say), you should be careful to buy
a printer whose print head gets replaced with every ink cartrige: infrequent
use can lead to the drying of the ink, both in the ink cartrige and in the
print head. The print heads you don't replace with the cartrige tend to cost
nearly as much as the printer (~$200 for an Epson Stylus 800) once the
warranty runs out (the third such repair, just after the warranty expired,
totalled one informant's Stylus 800). Be careful, check print head
replacement costs ahead of time, and run at least a cleaning cycle if you
don't actually print anything in a given week. (Conversely, toner starts out
dry, and ribbon ink won't evaporate for years...if you truly print only
rarely, but neither a dot matrix nor a laser makes sense, consider buying no
printer and taking your PostScript files to a copy shop...)

Nowadays, a lot of printers are moving away from parallel-port interfaces to
USB. This is a good idea, because USB devices announce themselves to the host
computer and can be automatically configured. Parallel ports (and serial
ports for that matter) are becoming obsolete. Many new PC motherboards no
longer include them.

Many printers (even some sub $100 models) now come with a network (10/100
Ethernet) interface. This make sharing them trivial, and also avoids having
to leave a desktop PC powered on so others (using notebooks perhaps) can
print to your printer. Therefore, such printers are worth considering in many
networked environments, including home networks.

In the near future, new motherboards may stop including parallel and serial
ports altogether. That's another good reason to go with a USB- or
Ethernet-capable printer.
-----------------------------------------------------------------------------

3.12. Power Protection

I strongly recommend that you buy a UPS to protect your hardware and data.
MOV-filtered power bars make nice fuses (they're cheap to replace), but
they're not enough. I have written a UPS HOWTO that provides more complete
coverage of what used to be in this section.
-----------------------------------------------------------------------------

3.13. Radio Frequency Interference

(Thanks to Robert Corbett <Robert.Corbett@Eng.Sun.COM> for contributing much
of this section)

Radio Frequency Interference (RFI) is a growing problem with PC-class
machines. Today's processor speeds are such that the electromagnetic noise
generated by a PC's circuitry in normal operation can degrade or jam radio
and TV reception in the neighborhood. Such noise is called Radio Frequency
Interference (RFI). Computers, as transmitting devices, are regulated by the
Federal Communications Commission (FCC).

FCC regulations recognize two classes of computer:

If a PC is to be used in a home or apartment, it must be certified to be FCC
class B. If it is not, neighbors have a legal right to prevent its use. FCC
class A equipment is allowed in industrial environments.

Many systems are not FCC class B. Some manufacturers build boxes that are
class B and then ship them with class A monitors or external disk drives.
Even the cables can be a source of RFI.

It pays to be cautious. For example, the Mag MX17F is FCC class B. There are
less expensive versions of the MX17 that are not. The Mag MX17 is a great
monitor (I wish I had one). It would be painful to own one and not be allowed
to use it.

An upgradeable system poses special problems. A system that is FCC class B
with a 33 MHz CPU might not be when the CPU is upgraded to a 50 or 66 MHz
CPU. Some upgrades require knockouts in the case to be removed. If a knockout
is larger than whatever replaces it, RFI can leak out through the gap.
Grounded metal shims can eliminate the leaks.

Even Class B systems don't mix well with wireless phonesets (not cellular
phones, but the kind with a base station and antennaed headset). You'll often
find a wireless phone hard to use withing 20 feet of a Class B machine.

To cut down on RFI, get a good metal case with tight joints, or at least make
sure any plastic one you buy has a conductive lining. You can also strip the
painted metal-to-metal contacting parts of paint so that there's good
conductive metal contact. Paint's a poor conductor in most cases, so you can
get some benefit from this.
-----------------------------------------------------------------------------

4. What To Optimize

4.1. First, add more memory

Max out your memory. Having lots of free memory will improve your
virtual-memory performance (and Unix takes advantage of extra memory more
effectively than Windows does). Fortunately, with RAM as cheap as it is now,
a gigabyte or three is unlikely to bust your budget even if you're
economizing.
-----------------------------------------------------------------------------

4.2. Bus and Disk speeds

Most people think of the processor as the most important choice in specifying
any kind of personal-computer system. But for typical job loads under Linux,
the processor type is nearly a red herring ?? it's far more important to
specify a capable system bus and disk I/O subsystem. If you don't believe
this, you may find it enlightening to keep top(1) running for a while as you
use your machine. Notice how seldom the CPU idle percentage drops below 90%!

It's true that after people upgrade their motherboards they often do report a
throughput increase. But this is often more due to other changes that go with
the processor upgrade, such as improved cache memory or an increase in the
clocking speed of the system's front-side bus (enabling data to get in and
out of the processor faster).

If you're buying for Linux on a fixed budget, it makes sense to trade away
some excess processor clocks to get a faster bus and disk subsystem. If
you're building a monster hot-rod, go ahead and buy that fastest available
processor ?? but once you've gotten past that gearhead desire for big
numbers, pay careful attention to bus speeds and your disk subsystem, because
that's where you'll get the serious performance wins. The gap between
processor speed and I/O subsystem throughput has only widened in the last
five years.

How does it translate into a recipe in 2007? Like this; if you're building a
hot rod,

*Do buy a machine with the fastest available "front-side" (e.g.
    processor-to-memory) bus.
   
*Do get a high-speed SCSI controller and the fastest SCSI disks you can
    get your hands on.
   

If you're economizing, you can back down on these. But in trading away SCSI
for SATA your reliability (expected time before failure) will drop. We'll
cover this in more detail in the next section.
-----------------------------------------------------------------------------

4.3. Disk Wars: SATA vs. SCSI

For the fastest disks you can find, pay close attention to average seek and
latency time. The former is an average time required to seek to any track;
the latter is the maximum time required for any sector on a track to come
under the heads, and is a function of the disk's rotation speed.

Of these, average seek time is much more important. When you're running Linux
or any other virtual-memory operating system, a one millisecond faster seek
time can make a really substantial difference in system throughput. Back when
PC processors were slow enough for the comparison to be possible (and I was
running System V Unix), it was easily worth as much as a 30MHz increment in
processor speed. Today the corresponding figure would probably be as much as
300MHz!

The manufacturers themselves avoid running up seek time on the
larger-capacity drives by stacking platters vertically rather than increasing
the platter size. Thus, seek time (which is proportional to the platter
radius and head-motion speed) tends to be constant across different
capacities in the same product line. This is good because it means you don't
have to worry about a capacity-vs.-speed tradeoff.

Disks of less than 40GB capacity simply aren't being manufactured anymore;
there's no margin in them. Our spies tell us that all major disk makers
retooled their lines a while back to produce 9GB unit platters, which are
simply being stacked 2N per spindle to produce ranges of drives with roughly
18GB increments of capacity.

Average drive latency is inversely proportional to the disk's rotational
speed. For years, most disks spun at 3600 rpm; most disks now spin at 7,200
or 10,000rpm, and high-end disks at 15,000 rpm. These fast-spin disks run
extremely hot; cooling is becoming a critical constraint in drive design.

Another basic decision is SATA vs. SCSI (the older IDE and EIDE buses are
obsolete). Either kind of disk costs about the same, but the premium for a
SCSI card varies all over the lot, partly because of price differences
between VLB and PCI SCSI cards and especially because many motherboard
vendors bundle a SATA chipset right on the system board. SCSI gives you
better speed and throughput and loads the processor less, a win for larger
disks and an especially significant consideration in a multi-user
environment; also it's more expandable. You can have at most four SATA
devices on a single controller. SCSI permits up to 7 (15 for wide SCSI).

Admittedly, the case for SCSI has eroded a bit since 2001; the new generation
of SATA drives is very fast, and controller cards now normally feature a
channel per drive and DMA (Direct Memory Access), so that some of of the
multi-user contention problems that used to dog IDE have diminished. At
10KRPM and below, SATA is as good as SCSI now (a painful admission for an
old-time IDE-hater like me), but at the 15KRPM high end SCSI still rules.

Of course, SATA is cheaper. Many motherboards have SATA right on board now;
if not, you'll pay maybe $15 for a SATA adapter board, as opposed to $200+
for the leading SCSI controller. Also, the cheap SCSI cabling most vendors
ship can be flaky. You have to use expensive high-class cables for
consistently good results. See Mark Sutton's horror story.
-----------------------------------------------------------------------------

4.3.1. Advantages of SCSI

For starters, SCSI is still at least 10%-15% faster than IDE/ATAPI running
flat out. Like Windows, SATA I is layered over a pile of ancestral designs
(ST-506 and IDE) that's antiquated and prone to failure under stress. For
example, on the Tyan K7 motherboards, there are known data-corruption
problems with the ATA controller in the presence of various DMA-using
bus-mastering cards.

SCSI, on the other hand, was designed from the beginning to scale up well to
high-speed, high-throughput systems. Because it's perceived as a 
"professional" choice, SCSI peripherals are generally better engineered than
IDE/ATAPI equivalents, and new high-performing drive technologies tend to
become available in SCSI first. You'll pay a few dollars more, but for Linux
the cost is well repaid in increased throughput and reliability.

The one aspect of SCSI that often gets overlooked is that it is a true
multitasking interface, thanks to the "disconnect/reconnect" sequence that
almost all SCSI hardware implements. With disconnect/reconnect, if a target
device has to perform some kind of time-consuming mechanical operation (e.g.,
a seek in the case of a disk or a medium position operation in the case of a
tape drive) the device will release control of the SCSI bus and allow it to
be used for some other operation. IDE/ATAPI has no such capability and is
often responsible for a system stall while a disk, CD-drive or tape drive
seeks to the desired medium position.

(Incidentally, SCSI performance can sometimes be improved by setting the ID
of the most frequently used disk drive as high as possible. The SCSI priority
pecking order is such that devices with higher ID's get first crack at the
bus when arbitration occurs during the selection phase.)

Rick's comments from 2001 are still apposite: "They call me a SCSI bigot. So
be it ?? but my hardware keeps being future-proof, I don't have to run
bizarre emulation layers to address CDRs, I never run low on IRQs or resort
to IRQ-sharing (on account of 3-4 ATA controllers each needing one, plus
special adapters for scanners, etc.), all my hard drives have hardware-level
hot-fix, all my hard disk/CD/tape/etc. devices support a stable standard
rather than this month's cheap extension kludge, and I don't have to worry
about adverse interactions at the hardware or driver levels from mixing ATA
and SCSI."

The cutting edge in SCSI devices is ultra wide LVD (low-voltage-differential)
SCSI drives with 320MB/sec transfer speed, running over a 68-pin cable (this
is twice as fast as the LVD-160 drives we used last time around). Vendors
often call LVD drives "SCSI-3", which is incorrect as most of these devices
don't have built-in support for the entire SCSI-3 protocol, and it would be
overdesign if they did (the extra commands are designed for use with CD and
multimedia devices).

Fast ultra LVD is a bit more expensive to support than the older versions of
SCSI (for which key words are "single-ended", describing the electrical
interface, and "narrow", describing the width of data transfers over the
older-style 50-pin connector). Thus, you're likely to find it only on hard
drives that are physically capable of doing high-speed data access off their
media; slower devices such as tapes and CD drives are normally still built
with the narrow single-ended variant.

The LVD-160 standard defines the SCSI bus, not the drive itself. Therefore,
when used with a single hard drive in a lightly loaded system (e.g., a Linux
machine supporting only one user) LVD-160 will have only a marginal effect on
system performance. This is because a single hard drive running flat out will
use only about 15-20 percent of the available bandwidth, as current drive
technology can manage no more than about 28-30 MB/sec off the platters, less
if a time consuming seek is involved. This rate could be higher, of course,
if a read request was pending and the drive had cached the desired data.
Where the LVD-160 bandwidth really becomes advantageous is in implementations
of multiple drives (e.g., RAID 5) and/or when activities produce the frequent
issue of drive access commands. The latter condition would be common in any
environment that supports a lot of users.

Current SCSI drives are not quite fast enough to flood more than half the
SCSI bus bandwidth, so you can have at least two drives on a single bus
pumping full speed without using it up. In reality, you don't keep drives
running full speed all the time, so you should be able to have 3-4 drives on
a bus before you really start feeling bandwidth crunch.
-----------------------------------------------------------------------------

4.3.2. SCSI Terminology

The following, by Ashok Singhal <ashoks@duckjibe.eng.sun.com> of Sun
Microsystems with additions by your humble editor, is a valiant attempt to
demystify SCSI terminology.

The terms "SCSI", "SCSI-2", and "SCSI-3" refer to three different
specifications. Each specification has a number of options. Many of these
options are independent of each other. I like to think of the main options
(there are others that I'll skip over because I don't know enough about them
to talk about them on the net) by classifying them into five categories:
-----------------------------------------------------------------------------

4.3.2.1. Logical: SCSI-1, SCSI-2, SCSI-3

This refers to the commands that the controllers understand. You'll no longer
see SCSI-1 in new hardware. SCSI-3 is a superset of SCSI-2 including commands
intended for CD-R and streaming multimedia devices.
-----------------------------------------------------------------------------

4.3.2.2. Electrical Interface

*single-ended (max cable length 6 meters)
   
*differential (max cable length 25 meters)
   

This option is independent of command set, speed, and path width.
Differential is less common but allows higher transfer speeds, better noise
immunity and longer cables. It's rare in SCSI-1 controllers.

You will normally see single-ended SCSI controllers on low-speed devices such
as tapes and CD drives, and differential SCSI on hard drives (look for the
specification LVD which means "low-voltage differential").

Nowadays most controllers support both electrical interfaces, but if you mix
LVD with single-ended on the same chain, the whole chain will fall back to
single-ended (and possibly halve the speed of the faster devices).
-----------------------------------------------------------------------------

4.3.2.3. Handshake

*Asynchronous (acknowledge each word (8, 16 or 32 bits) transferred.
   
*Synchronous (multiple-word transfers permitted between ACKS).
   

Synchronous is faster. This mode is negotiated between controller and device;
modes may be mixed on the same bus. This is independent of command set, data
width, and electrical interface.
-----------------------------------------------------------------------------

4.3.2.4. Synchronous Speed (does not apply for asynchronous option)

Normal transfer speed is 5 megabytes/sec. The "fast" option (10 mb/sec) is
defined only in SCSI-2 and SCSI-3. Fast-20 (or "Ultra") is 20 mb/sec; Fast-40
(or "Ultra-2") is 40MB/sec. The fast options basically defines shorter timing
parameters such as the assertion period and hold time.

The parameters of the synchronous transfer are negotiated between each target
and initiator so different speed transfers can occur over the same bus.
-----------------------------------------------------------------------------

4.3.2.5. Path width

The standard SCSI data path is 8 bits wide. The "wide" option exploits a 16-
or 32-bit data path (uses 68-pin rather than 50-pin data cables). You also
get 4-bit rather than 3-bit device IDs, so you can have up to 16 devices. The
wide option doubles or quadruples your transfer rate, so for example a
fast-20/wide SCSI link using 16 bits transfers 40mb/sec.

What are those "LUN" numbers you see when you boot up? Think of them as
sub-addresses on the SCSI bus. Most SCSI devices have only one "logical"
device inside them, thus they're LUN zero. Some SCSI devices can, however,
present more than one separate logical unit to the bus master, with different
LUNs (0 through 7). The only context in which you'll normally use LUNs is
with CD-ROM juke boxes. Some have been marketed that offer up to 7 CD-ROMS
with one read head. These use the LUN to differentiate which disk to select.

(There's history behind this. Back in the days of EISA, drives were supposed
to be under the control of a separate SCSI controller, which could handle up
to 7 such devices (15 for wide SCSI). These drives were to be the Logical
Units; hence the LUN, or Logical Unit Number. Then, up to 7 of these SCSI
controllers would be run by the controller that we today consider the SCSI
controller. In practice, hardware cost dropped so rapidly, and capability
increased so rapidly, it became more logical to embed the controller on the
drive.)
-----------------------------------------------------------------------------

4.3.3. Avoiding Pitfalls

Here are a couple of rules and heuristics to follow:

Rule 1: Total SCSI cable length (both external and internal devices) must not
exceed six meters. For modern Ultra SCSI (with its higher speed) cut that to
three feet!

It's probably not a good idea to cable 20MB/s or faster SCSI devices
externally at all. If you must, one of our informants advises using a Granite
Digital "perfect impedance" teflon cable (or equivalent); these cables
basically provide a near-perfect electrical environment for a decent price,
and can be ordered in custom configurations if needed.

A common error is to forget the length of the ribbon cable used for internal
devices when adding external ones (that is, devices chained to the SCSI
board's external connector).

Rule 2: Both ends of the bus have to be electrically terminated.

On older devices this is done with removable resistor packs ?? typically
8-pin-inline widgets, yellow or blue, that are plugged into a plastic
connector somewhere near the edge of the PCB board on your device.
Peripherals commonly come with resistor packs plugged in; you must remove the
packs on all devices except the two end ones in the physical chain.

Newer devices advertised as having "internal termination" have a jumper or
switch on the PCB board that enables termination. These devices are
preferable, because the resistor packs are easy to lose or damage.

Rule 3: No more than seven devices per chain (fifteen for Wide SCSI).

There are eight SCSI IDs per controller. The controller reserves ID 7 or 15,
so your devices can use IDs 0 through 6 (or 0 through 14, wide). No two
devices can share an ID; if this happens by accident, neither will work.

The conventional ID assignments are: Primary hard disk = ID 0, Secondary hard
disk = ID 1, Tape = ID 2. Some Unixes (notably SCO) have these wired in. You
select a device's ID with jumpers on the PCB or a thumbwheel.

SCSI IDs are completely independent of physical device chain position.

Heuristic A: You'll have fewer hassles if all your cables are made by the
same outfit. (This is due to impedence reflections from minor mismatches. You
can get situations where cable A will work with B, cable B will work with C,
but A and C aren't happy together. It's also non-commutative. The fact that
`computer to A to B' works doesn't mean that `computer to B to A' will work.

Heuristic B. Beware Cheap SCSI Cables!

Mark Sutton tells the following instructive horror story in a note dated 5
Apr 1997:

I recently added an additional SCSI hard drive to my home machine. I bought
an OEM packaged Quantum Fireball 2 gig SCSI drive (meaning, I bought a drive
in shrinkwrap, without so much as mounting hardware or a manual. Thank God
for Quantum's web page or I would have had no idea how to disable termination
or set the SCSI ID on this sucker. Anyway, I digress...). I stuck the drive
in an external mounting kit that I found in a pile of discarded computer
parts at work and my that boss said I could have. (All 5 of my internal bays
were full of devices.)

Anyway, I had my drive, and my external SCSI mounting kit, I needed a cable.

I went into my friendly local CompUSA in search of a SCSI cable, and
side-by-side, on two hooks, were two "identical" SCSI cables. Both were 3
feet. Both had Centronics to Centronics connectors, both were made by the
same manufacturer. They had slightly different model numbers. One was $16.00,
one was $30.00. Of course, I bought the $16 cable.

Bad, I say, bad bad mistake. I hooked this sucker up like so:
 +--------+   +-------+     +-----------+     +-------+                      
 |Internal|---|Adaptec|-----|New Quantum|-----|UMAX   |                      
 |Devices |   |1542CF |  ^  |  Disk     |  ^  |Scanner|                      
 +--------+   +-------+  |  +-----------+  |  +-------+                      
                         |                 |                                 
                    New $16 cable   Cable that came                          
                                      with scanner.                          

Shortly after booting, I found that data all over my old internal hard drive
was being hosed. This was happening in DOS as well as in Linux. Any disk
access on either disk was hosing data on both disks, attempts to scan were
resulting in corrupted scans *and* hosing files on the hard disks. By the
time I finished swapping cables around, and checking terminations and
settings, I had to restore both Linux and DOS from backups.

I went back to CompUSA, exchanged the $16 cable for the $30 one, hooked it up
and had no more problems.

I carefully examined the cables and discovered that the $30 cable contained
24 individual twisted pairs. Each data line was twisted with a ground line.
The $16 cable was 24 data wires with one overall grounded shield. Yet, both
of these cables (from the same manufacturer) were being sold as SCSI cables!

You get what you pay for.

(Another correspondent guesses that the cheap cable probably said "Macintosh"
on it. The Mac connector is missing most of its ground pins.)
-----------------------------------------------------------------------------

4.3.4. More Resources

There's a USENET [http://www.cis.ohio-state.edu/hypertext/faq/usenet/scsi-faq
/top.html]  SCSI FAQ. Also see the home page of the T10 committee that writes
SCSI standards.

There is a large searchable database of hard disk and controller information
at the PC DISK Hardware Database.
-----------------------------------------------------------------------------

4.4. Tuning Your I/O Subsystem

(This section comes to us courtesy of Perry The Cynic, <perry@sutr.cynic.org
>; it was written in 1998. My own experience agrees pretty completely with
his. I have revised the numbers in it since to reflect more recent
developments.)

Building a good I/O subsystem boils down to two major points: pick matched
components so you don't over-build any piece without benefit, and construct
the whole pipe such that it can feed what your OS/application combo needs.

It's important to recognize that "balance" is with respect to not only a
particular processor/memory subsystem, but also to a particular OS and
application mix. A Unix server machine running the whole TCP/IP server suite
has radically different I/O requirements than a video-editing workstation.
For the "big boys" a good consultant will sample the I/O mix (by reading
existing system performance logs or taking new measurements) and figure out
how big the I/O system needs to be to satisfy that app mix. This is not
something your typical Linux buyer will want to do; for one, the application
mix is not static and will change over time. So what you'll do instead is
design an I/O subsystem that is internally matched and provides maximum
potential I/O performance for the money you're willing to spend. Then you
look at the price points and compare them with those for the memory
subsystem. That's the most important trade-off inside the box.

So the job now is to design and buy an I/O subsystem that is well matched to
provide the best bang for your buck. The two major performance numbers for
disk I/O are latency and bandwidth. Latency is how long a program has to wait
to get a little piece of random data it asked for. Bandwidth is how much
contiguous data can be sent to/from the disk once you've done the first
piece. Latency is measured in milliseconds (ms); bandwidth in megabytes per
second (MB/s). Obviously, a third number of interest is how big all of your
disks are together (how much storage you've got), in Gigabytes (GB).

Within a rather big envelope, minimizing latency is the cat's meow. Every
millisecond you shave off effective latency will make your system feel
significantly faster. Bandwidth, on the other hand, only helps you if you
suck a big chunk of contiguous data off the disk, which happens rarely to
most programs. You have to keep bandwidth in mind to avoid mis-matching
pieces, because (obviously) the lowest usable bandwidth in a pipe constrains
everything else.

I'm going to ignore IDE. IDE is no good for multi-processing systems, period.
You may use an IDE CD-ROM if you don't care about its performance, but if you
care about your I/O performance, go SCSI. (Beware that if you mix an IDE
CD-ROM with SCSI drives under Linux, you'll have to run a SCSI emulation
layer that is a bit flaky.)

Let's look at the disks first. Whenever you seriously look at a disk, get its
data sheet. Every reputable manufacturer has them on their website; just read
off the product code and follow the bouncing lights. Beware of numbers (`<
12ms fast!') you may see in ads; these folks often look for the lowest/
highest numbers on the data sheet and stick them into the ad copy. Not
dishonest (usually), but ignorant.

What you need to find out for a disk is:

 1. What kind of SCSI interface does it have? Look for "fast", "ultra", and
    "wide". Ignore disks that say "fiber" (this is a specialty physical layer
    not appropriate for the insides of small computers). Note that you'll
    often find the same disk with different interfaces.
   
 2. What is the "typical seek" time (ms)? Make sure you get "typical", not
    "track-to-track" or "maximum" or some other measure (these don't relate
    in obvious ways, due to things like head-settling time).
   
 3. What is the rotational speed? This is typically 4500, 5400, 7200, 10000,
    or 15000 rpm (rotations per minute). Also look for "rotational latency"
    (in ms). (In a pinch, average rotational latency is approx. 30000/rpm in
    milliseconds.)
   
 4. What is the ??media transfer rate?? or speed (in MB/s)? Many disks will
    have a range of numbers (say, 7.2-10.8MB/s). Don't confuse this with the
    "interface transfer rate" which is always a round number (10 or 20 or
    40MB/s) and is the speed of the SCSI bus itself.
   

These numbers will let you do apple-with-apples comparisons of disks. Beware
that they will differ on different-size models of the same disk; typically,
bigger disks have slower seek times.

Now what does it all mean? Bandwidth first: the `media transfer rate' is how
much data you can, under ideal conditions, get off the disk per second. This
is a function mostly of rotation speed; the faster the disk rotates, the more
data passes under the heads per time unit. This constrains the sustained
bandwidth of this disk.

More interestingly, your effective latency is the sum of typical seek time
and rotational latency. So for a disk with 8.5ms seek time and 4ms rotational
latency, you can expect to spend about 12.5ms between the moment the disk
`wants' to read your data and the moment when it actually starts reading it.
This is the one number you are trying to make small. Thus, you're looking for
a disk with low seek times and high rotation (RPM) rates.

For comparison purposes, the first hard drive I ever bought was a 20MB drive
with 65ms seek time and about 3000RPM rotation. A floppy drive has about
100-200ms seek time. A CD-ROM drive can be anywhere between 120ms (fast) and
400ms (slow). The best IDE harddrives have about 10-12ms and 5400 rpm. The
best SCSI harddrive I know (the Fujitsu MAM) runs 3.9ms/15000rpm.

Fast, big drives are expensive. Really big drives are very expensive. Really
fast drives are pretty expensive. On the other end, really slow, small drives
are cheap but not cost effective, because it doesn't cost any less to make
the cases, ship the drives, and sell them.

In between is a ??sweet spot?? where moving in either direction (cheaper or
more expensive) will cost you more than you get out of it. The sweet spot
moves (towards better value) with time. Right now (early 2004), it's about at
36GB drives, 6ms, 10000rpm, ultra2 SCSI. If you can make the effort, go to
your local computer superstore and write down a dozen or so drives they sell
??naked??. (If they don't sell at least a dozen hard drives naked, find
yourself a better store. Use the Web, Luke!) Plot cost against size, seek and
rotational speed, and it will usually become pretty obvious which ones to get
for your budget.

Do look for specials in stores; many superstores buy overstock from
manufacturers. If this is near the sweet spot, it's often surprisingly
cheaper than comparable drives. Just make sure you understand the warranty
procedures.

Note that if you need a lot of capacity, you may be better off with two (or
more) drives than a single, bigger one. Not only can it be cheaper but you
end up with two separate head assemblies that move independently, which can
cut down on latency quite a bit (see below).

Once you've decided which kind of drive(s) you want, you must decide how to
distribute them over one or more SCSI buses. Yes, you may want more than one
SCSI bus. (My current desktop machine has three.) Essentially, the trick is
to make sure that all the disks on one bus, talking at the same time, don't
exceed the capacity of that bus. At this time, I can't recommend anything but
an Ultra/Wide SCSI controller. This means that the attached SCSI bus can
transfer data at up to 40MB/s for an Ultra/Wide disk, 20MB/s for an Ultra/
narrow disk, and 10MB/s for a `fast SCSI' disk. These numbers allow you do do
your math: an 8MB/s disk will eat an entire bus on its own if it's ??fast??
(10MB/s). Three 6MB/s ultra/narrow disks fit onto one bus (3x6=18MB/s<20MB/
s), but just barely. Two ultra/wide Cheetahs (12.8MB/s) will share an (ultra/
wide) bus (25.6<40), but they would collide on an ultra/narrow bus, and any
one Cheetah would be bandwidth constrained on a (non-ultra) `fast' bus (12.8
> 10).

If you find that you need two SCSI buses, you can go with ??dual channel??
versions of many popular SCSI controller cards (including the Adaptec). These
are simply two controllers on one card (thus taking only one PCI slot). This
is cheaper and more compact than two cards; however, on some motherboards
with more than 3 PCI slots, using two cards may be somewhat faster (ask me
what a PCI bridge is :-).

SCSI performance can sometimes be improved by setting the ID of the most
frequently used disk drive as high as possible. The SCSI priority pecking
order is such that devices with higher ID's get first crack at the bus when
arbitration occurs during the selection phase.

How do you deal with slow SCSI devices ?? CD-ROMS, scanners, tape drives,
etc.? If you stick these onto a SCSI bus with fast disks, they will slow down
things a bit. You can either accept that (as in "I hardly ever use my scanner
anyway"), or stick them onto a separate SCSI bus off a cheap controller card.
Or you can (try to) get an ATA version to stick onto that inevitable IDE
interface on your motherboard. The same logic applies to disks you won't
normally use, such as removables for data exchange.

If you find yourself at the high end of the bandwidth game, be aware that the
theoretical maximum of the PCI bus itself is 132MB/s. That means that a dual
ultra/wide SCSI controller (2x40MB/s) can fill more than half of the PCI
bus's bandwidth, and it is not advised to add another fast controller to that
mix. As it is, your device driver better be well written, or your entire
system will melt down (figuratively speaking).

Incidentally, all of the numbers I used are ??optimal?? bandwidth numbers.
The real scoop is usually somewhere between 50-70% of nominal, but things
tend to cancel out ?? the drives don't quite transfer as fast as they might,
but the SCSI bus has overhead too, as does the controller card.

Whether you have a single disk or multiple ones, on one or several SCSI
buses, you should give careful thought to their partition layout. Given a set
of disks and controllers, this is the most crucial performance decision
you'll make.

A partition is a contiguous group of sectors on the disk. Partitioning
typically starts at the outside and proceeds inwards. All partitions on one
disk share a single head assembly. That means that if you try to overlap I/O
on the first and last partition of a disk, the heads must move full stroke
back and forth over the disk, which can radically increase seek time delays.
A partition that is in the middle of a partition stack is likely to have best
seek performance, since at worst the heads only have to move half-way to get
there (and they're likely to be around the area anyway).

Whenever possible, split partitions that compete onto different disks. For
example, /usr and the swap should be on different disks if at all possible
(unless you have outrageous amounts of RAM).

Another wrinkle is that most modern disks use `zone sectoring'. The upshot is
that outside partitions will have higher bandwidth than inner ones (there is
more data under the heads per revolution). So if you need a work area for
data streaming (say, a CD-R pre-image to record), it should go on an outside
(early numbered) partition of a fast-rotating disk. Conversely, it's a good
convention to put rarely-used, performance-uncritical partitions on the
inside (last).

Another note concerns SCSI mode pages. Each (modern) SCSI disk has a small
part of its disk (or a dedicated EEPROM) reserved for persistent
configuration information. These parameters are called ??mode pages??, for
the mechanism (in the SCSI protocol) for accessing them. Mode page parameters
determine, among others, how the disk will write-cache, what forms of error
recovery it uses, how its RAM cache is organized, etc. Very few configuration
utilities allow access to mode page parameters (I use FWB Toolkit on a Mac ??
it's simply the best tool I know for that task), and the settings are usually
factory preset for, uh, Windows 95 environments with marginal hardware and
single-user operation. Particularly the cache organization and disconnect/
reconnect pages can make a tremendous difference in actual performance.
Unfortunately there's really no easy lunch here - if you set mode page
parameters wrong, you can screw up your data in ways you won't notice until
months later, so this is definitely `no playing with the pushebuttons'
territory.

Ah yes, caches. There are three major points where you could cache I/O
buffers: the OS, the SCSI controller, and the on-disk controller. Intelligent
OS caching is by far the biggest win, for many reasons. RAM caches on SCSI
controller cards are pretty pointless these days; you shouldn't pay extra for
them, and experiment with disabling them if you're into tinkering.

RAM caches on the drives themselves are a mixed bag. At moderate size
(1-2MB), they are a potential big win for Windows 95/98, because Windows has
stupid VM and I/O drivers. If you run a true multi-tasking OS like Linux,
having unified RAM caches on the disk is a significant loss, since the
overlapping I/O threads kick each other out of the cache, and the disk ends
up performing work for nothing.

Most high-performance disks can be reconfigured (using mode page parameters,
see above) to have `segmented' caches (sort of like a set-associative memory
cache). With that configured properly, the RAM caches can be a moderate win,
not because caching is so great on the disk (it's much better in the OS), but
because it allows the disk controller more flexibility to reschedule its I/O
request queue. You won't really notice it unless you routinely have >2 I/O
requests pending at the SCSI level. The conventional wisdom (try it both
ways) applies.

And finally I do have to make a disclaimer. Much of the stuff above is
shameless simplification. In reality, high-performance SCSI disks are very
complicated beasties. They run little mini-operating systems that are most
comfortable if they have 10-20 I/O requests pending at the same time. Under
those circumstances, the amortized global latencies are much reduced, though
any single request may experience longer latencies than if it were the only
one pending. The only really valid analysis are stochastic-process models,
which we really don't want to get into here. :-)
-----------------------------------------------------------------------------

5. But What If I'm Economizing?

If you are economizing, here's a simple rule:

*Do buy a CPU/motherboard one or two levels lower than commercial state of
    the art.
   

For best value, look in the middle of the current range of available
processors. On the desktop, in late 2007, that means a CPU costing perhaps
$75 to $200, not the latest and greatest quad core marvels selling for
several times that!

Why? Because of the way manufacturers' price-performance curves are shaped.
The top-of-line system is generally boob bait for corporate executives and
other people with more money than sense. Chances are the system design is new
and untried ?? if you're at the wrong point in the technology cycle, the chip
may even be a pre-production sample, or an early production stepping with
undiscovered bugs like the infamous FDIV problem in early Pentiums. You don't
need such troubles. Better to go with a chip/motherboard combination that's
been out for a while and is known good. It's not like you really need the
extra speed, after all.

Besides, if you buy one of these gold-plated systems, you're only going to
kick yourself three months later when the price plunges by 30%. Further down
the product line there's been more real competition and the manufacturer's
margins are already squeezed. There's less room for prices to fall, so you
won't watch your new toy lose street value so fast. Its price will still
drop, but it won't plummet sickeningly.

Again, bear in mind that the cheapest processor you can buy new today is
plenty fast enough for Linux. So if dropping back a speed level or two brings
you in under budget, you can do it with no regrets.

Consider SATA hard drives instea of SCSI. Consider one drive rather than two.
This will reduce overall system performance somewhat, but the cost saving as
a fraction of total system cost is often substantial.

Another easy economy measure is looking for repaired or reconditioned parts
with a warranty. These are often as good as new, and much cheaper.

Your display is one of the areas where pinching pennies is not a good idea.
You're going to be looking at that display for hours on end. You are going to
be using the screen real estate constantly. Buy the best quality, largest
screen you possibly can ?? it will be worth it.

Similarly, do not reduce the amount of RAM in your system too far. A minimum
of 2GB of RAM is helpful in desktop systems today.
-----------------------------------------------------------------------------

6. Noise Control and Heat Dissipation

An increasingly critical aspect of machine design is handling the waste heat
and acoustic noise of operation. This may seem like a boring subject, but
cooling is a centrally important one if you want your machine to last ??
because thermal stress from the electronics' own waste heat is almost
certainly what will kill it. You want that fatal moment to happen later
rather than sooner. On the other hand, cooling makes acoustic noise, which
human beings don't tolerate well.

This tradeoff bites harder than you think; it's the fundamental reason that,
despite my money-is-no-object premise in the Ultimate Linux Box artcles, I
didn't go to relatively exotic technologies like liquid-cooled overclocking
or RAID disk arrays for a performance boost. Sure, they may initially look
attractive ?? but overclocked chips and banks of disk drives require massive
cooling with lots of moving parts, and it's not good to be trying to do
creative work like programming with anything that sounds quite so much like
an idling jet engine sitting beside one's desk.

In 2001 we had already reached the point at which the thermal load vs.
cooling-noise tradeoff is the effective limiting factor in the performance of
personal machines. Ten years ago, even low-end and medium "server" machines
differed from personal-PC designs in fairly important ways (different
processor and bus types, different speed ranges, etc.) Nowadays specialized
server architectures are in retreat at the high end of the market and
everything else looks like a PC. And the difference between a "PC" and a
"server" is mainly that servers live in server rooms, and are allowed to have
monster cases with lots of noisy fans.

So how do we manage this tradeoff for a personal, desktop or desk-side
machine? Careful choice of components and being willing to pay some price
premium for cool-running and low-noise characteristics can help a lot. Even
exceptionally clueful system integrators can't generally afford to do this,
because they're under constant competitive pressure to cut price and costs by
using generic components.

Reducing expected noise and heat in a design call for different strategies.
It's relatively easy to find decibel figures for the noisemaking parts in a
PC design. And, once you know a little basic audiometry and a few basic rules
of thumb, it's not hard to form a fair estimate of your design's noisiness.
Estimating a design's heat dissipation is harder, partly because the
waste-heat emission of a PC's subsystems tends to vary in a more complex way
than the acoustic emissions of the mechanical parts. This means that you can
and should try to design ahead for low noise, but on the other hand expect to
have to monitor for heat-dissipation problems in your prototype and solve
them by building in more cooling.

Here's the basic audiometry you need to know to control your design's noise
emissions:

Sound is measured in decibels, abbreviated dB, relative to the threshold of
audibility, "A". (Thus, sound levels above that threshold are written "dBA".)
The scale is logarithmic, with every 3dB increment roughly doubling sound
intensity.

For sounds that are not phase-related, decibel levels add as a logarithmic
sum. Thus if X and Y are uncorrelated sound sources,


dBA(X+Y)=10*log(10^(dBA(X)/10)+10^(dBA(Y)/10))

A consequence of the above formula is that dBA(X + Y) cannot be more than 3dB
above the greater of dBA(X) and dBA(Y) for uncorrelated sources (6dB for
perfectly correlated ones).

Sound from a point source decays by an inverse-square law, roughly 6dB for
each doubling of distance.

Important thresholds on the decibel scale:

0 dBA
    Threshold of hearing
   
20 dBA
    Rustling leaves, quiet living room
   
30 dBA
    Quiet office
   
40 dBA
    Quiet conversation
   
45 dBA
    Threshold of distraction, according to EPA
   
50 dBA
    Quiet street, average office noise
   
60 dBA
    Normal conversation (1 foot distance)
   
70 dBA
    Inside car
   
75 dBA
    Loud singing (3 feet)
   
80 dBA
    Typical home-stereo listening level
   

The acoustic noise emitted by PCs is normally a combination of white noise
produced by airflow, high-frequency noise produced by bearing friction in
drive spindles and fans, and the constant frequency "blade passing" noise
that all propellers emit (the latter is often more intense than white noise
and bearing whine).

The best low-noise ball-bearing case fans emit around 20dBA. Typical
sleeve-bearing fans emit 30-50dBA.

According to the indispensable [http://tomshardware.com/] Tom's Hardware
site, you can expect to cut at least 5dB off the interior noise level of the
computer with a good choice of case. We'll improve on that by adding
sound-absorbing material to the interior.
-----------------------------------------------------------------------------

7. Special Considerations When Buying Laptops

Up until about 1999 the laptop market was completely crazy. The technology
was in a state of violent flux, with "standards" phasing in and out and
prices dropping like rocks. Things are beginning to settle out a bit more
now.

One sign of this change is that there are now a couple of laptop lines that
are clear best-of-breeds for reasons having as much to do with good
industrial design and ergonomics as the technical details of the processor
and display.

In lightweight machines, I'm a big fan of the Sony VAIO line. I owned one
from early 1999 until it physically disintegrated under the rigors of travel
in late 2000, and could hardly imagine switching. They weigh 3.5 pounds, give
you an honest 3 hours of life per detachable battery pack, have a very nice
1024x768 display, and are just plain pretty. Their only serious drawback is
that they're not rugged, and often fall apart after a year or so of use.

If you want a full-power laptop that can compete with or replace your desktop
machine, the Lenovo (formerly IBM) ThinkPad line is the bomb. Capable,
rugged, and nicely designed. I now use a ThinkPad X61, the lightest and
smallest machine in the line, and like it a lot.

These machines are not cheap, though. If you're trying to save money by
buying a no-name laptop, here are things to look for:

First: despite what you may believe, the most important aspect of any laptop
is not the CPU, or the disk, or the memory, or the screen, or the battery
capacity. It's the keyboard feel, since unlike in a PC, you cannot throw the
keyboard away and replace it with another one unless you replace the whole
computer. Never buy any laptop that you have not typed on for a couple hours.
Trying a keyboard for a few minutes is not enough. Keyboards have very subtle
properties that can still affect whether they mess up your wrists.

A standard desktop keyboard has keycaps 19mm across with 7.55mm between them.
If you plot frequency of typing errors against keycap size, it turns out
there's a sharp knee in the curve at 17.8 millimeters. Beware of "kneetop"
and "palmtop" machines, which squeeze the keycaps a lot tighter and typically
don't have enough oomph for Unix anyway; you're best off with the "notebook"
class machines that have full-sized keys.

Second: with present flatscreens, 1920x1200 color is the best you're going to
do (and that is on a 17in widescreen, which translates to a large notebook.
On normal size notebooks, a maximum of 1440x900 is more common). On travel
machines like the Lenovo X serties, you're still stuck with 1024x768. If you
want more than that (for X, for example) you have to either fall back to a
desktop or make sure there's an external-monitor port on the laptop (and many
laptops won't support higher resolution than the flatscreen's).

Third: about those vendor-supplied time-between-recharge figures; don't
believe them. They collect those from a totally quiescent machine, sometimes
with the screen or hard disk turned off. Under Windows, you'd be lucky to get
half the endurance they quote; under Unix, which hits the disk more often, it
may be less yet. Figures from magazine reviews are more reliable.

Fourth: You can now avoid many of the driver hassles involved in getting some
devices on your notebook to work (or week well) under Linux by purchasing a
notebook with Linux pre-installed. Dell has recently started to make noise in
this regard in the Linux community. Taking this approach limits the set of
notebooks you can consider, but the one you get is likely to "just work"
(including sound, useful capabilities like suspend/resume, and even
hotplugging of external displays and projectors) to a much higher degree
under Linux than others.
-----------------------------------------------------------------------------

8. How to Buy

8.1. When to Buy

It used to be that good configurations for Unix were what the market called
??server?? machines, with beefed-up I/O subsystems and fast buses. No longer;
today's ??servers?? are monster boxes with multiple power supplies and
processors, gigabytes of memory, and industrial-grade air cooling ??they're
not really suitable as personal machines. A typical SCSI desktop workstation
is as much as you'll need.

Prices keep dropping, so there's a temptation to wait forever to buy. A good
way to cope with this is to configure your system on paper, get a couple of
initial estimates, then set a trigger price, below the lowest one, at what
you're willing to pay. Then watch and wait. When the configuration cost hits
your trigger price, place your order.

The advantage of this method is that it requires you to settle in your mind,
well in advance, what you're willing to pay for what you're getting. That
way, you'll buy at the earliest time you should, and won't stress too much
out afterwards as it depreciates.

Before you shop, do your homework. Publications like "Computer Shopper" (and
their web site at [http://www.computershopper.com]  http://
www.computershopper.com) are invaluable for helping you get a feel for prices
and what clonemakers are doing. Another excellent site is [http://
www.computeresp.com] ComputerESP.
-----------------------------------------------------------------------------

8.2. Where to Buy

The most important where-to-buy advice is negative. Do not go to a
traditional, business-oriented storefront dealership. Their overheads are
high. So are their prices.

Especially, run ??do not walk ??away from any outfit that trumpets ??business
solutions??. This is marketing code for the kind of place that will justify a
heavy price premium by promising after-sale service and training which, nine
times out of ten, will turn out to be nonexistent or incompetent. Sure,
they'll give you plush carpeting and a firm handshake from a guy with too
many teeth and an expensive watch ??but did you really want to pay for that?

There are two major alternatives to storefront dealerships and one minor one.
The major ones are mail order and computer superstores. The minor one is
computer fairs.
-----------------------------------------------------------------------------

8.3. Computer Fairs

I used to be a big fan of hole-in-the-wall stores run by immigrants from the
other side of the International Date Line, but most of those places have been
driven out of the regular retail game by the superstores. If you still have
one in your neighborhood, you're lucky. I do, as it happens, but that is now
unusual; the only place you normally find diaspora Chinese and Indians
selling cheap PCs over the counter anymore is at computer fairs. (Usually
they're doing it to publicize an Internet/mail-order business.)

You can find good loss-leader deals on individual parts at these fairs
(they're especially good places to buy disk drives cheap). But I call them a
minor alternative because it's hard to get a custom SCSI-based configuration
tuned for Unix built for you at a fair. So you end up, effectively, back in
the mail-order or Web channel.
-----------------------------------------------------------------------------

8.4. Mail Order

Internet buying makes a lot of sense today for anyone with more technical
savvy than J. Random Luser in a suit. Even from no-name vendors, parts and
system quality tend to be high and consistent, so conventional dealerships
don't really have much more to offer than a warm fuzzy feeling. Furthermore,
competition has become so intense that even Internet/mail-order vendors today
have to offer not just lower prices than ever before but warranty and support
policies of a depth that would have seemed incredible a few years back. For
example, many bundle a year of on-site hardware support with their medium-
and high-end "business" configurations for a very low premium over the bare
hardware.

Note, however, that assembling a system yourself out of parts is not likely
to save you money over dealing with the Internet/mail-order systems houses.
You can't buy parts at the volume they do; the discounts they command are
bigger than the premiums reflected in their prices. The lack of any system
warranty or support can also be a problem even if you're expert enough to do
the integration yourself ?? because you also assume all the risk of defective
parts and integration problems.

Watch out for dealers (Spectrum Trading for one) who charge ridiculous
shipping fees. One of our spies reports he bought a hotswappable hard disc
drive tray that weighed about 3 lbs. and cost $250 and they charged $25 to
ship it UPS groud.

Don't forget that (most places) you can avoid sales tax by buying from an
out-of-state outfit, and save yourself 6-8% depending on where you live. If
you live near a state line, buying from a local outfit you can often win,
quite legally, by having the stuff shipped to a friend or relative just over
it. Best of all is a buddy with a state-registered dealer number; these
aren't very hard to get and confer not just exemption from sales tax but
(often) whopping discounts from the vendors. Hand him a dollar afterwards to
make it legal.

(Note: I have been advised that you shouldn't try the latter tactic in
Florida ??they are notoriously tough on "resale license" holders).

(Note II: The Supreme Court has ruled that states may not tax out-of-state
businesses under existing law, but left the way open for Congress to pass
enabling legislation. Let's hope the mail-order industry has good lobbyists.)
-----------------------------------------------------------------------------

8.5. Computer Superstores

Big chain superstores like CompUSA and Circuit City give you a reasonable
alternative to the Web. And there are good reasons to explore it ?? these
stores buy and sell at volumes that allow them to offer prices not far above
the Web. (They make back a lot of their margin on computer games and small
accessories like mouse pads, cables, and floppy disks.)

Note, however: Avoid Best Buy. Horror stories about them are legion ??
predatory salescritters, incompetent service, routine bait-and-switch
tactics.

One thing you should not buy remotely if you can avoid it is a monitor.
Monitors are subject to significant quality variations even within the same
make and model. Flatscreens haver this [roblem less than CRTs did, but you
don't want a flatscreen with dead pixels. So buy your monitor face-to-face,
picking the best out of three or four.

Another good argument for buying at a superstore is that you may have to pay
return postage if you ship a system back to the vendor. On a big, heavy
system, this can eat your initial price savings.

The only major problem with superstores is that the salespeople who staff
them aren't very bright or very clueful (it's a sort of Darwinian
reverse-selection effect; these are the guys who are fascinated by computer
technology but not smart enough to be techies). Most of them don't know from
Linux and are likely to push things like two-button mice that you can't use.
Use caution and check your system manifest.

But if you shop carefully and don't fall for one of their name-brand
"prestige" systems, you can get prices comparable to Internet/mail-order with
the comfort of knowing there's a trouble desk you can drive back to in a
pinch. (Also, you can see your monitor before you buy!)
-----------------------------------------------------------------------------

8.6. Other Buying Tips

You can often get out of paying tax just by paying cash, especially at
computer shows. You can always say you're going to ship the equipment out of
the state.

A lot of vendors bundle Windows and variable amounts of apps with their
hardware. If you tell them to lose all this useless cruft they may shave $50
or $100 off the system price.
-----------------------------------------------------------------------------

9. Questions You Should Always Ask Your Vendor

9.1. Minimum Warranty Provisions

The weakest guarantee you should settle for in the mail-order market should
include:

*72-hour burn-in to avoid that sudden infant death syndrome. (Also, try to
    find out if they do a power-cycling test and how many repeats they do;
    this stresses the hardware much more than steady burn-in.)
   
*30 day money-back guarantee. Watch out for fine print that weakens this
    with a restocking fee or limits it with exclusions.
   
*1 year parts and labor guarantee (some vendors give 2 years).
   
*1 year of 800 number tech support (many vendors give lifetime support).
   

Additionally, many vendors offer a year of on-site service free. You should
find out who they contract the service to. Also be sure the free service
coverage area includes your site; some unscrupulous vendors weasel their way
out with "some locations pay extra", which translates roughly to "through the
nose if you're further away than our parking lot".

If you're buying store-front, find out what they'll guarantee beyond the
above. If the answer is "nothing", go somewhere else.
-----------------------------------------------------------------------------

9.2. Documentation

Ask your potential suppliers what kind and volume of documentation they
supply with your hardware. You should get, at minimum, operations manuals for
the motherboard and each card or peripheral; also an IRQ list. Skimpiness in
this area is a valuable clue that they may be using no-name parts from Upper
Baluchistan, which is not necessarily a red flag in itself but should prompt
you to ask more questions.
-----------------------------------------------------------------------------

9.3. A System Quality Checklist

There are various cost-cutting tactics a vendor can use which bring down the
system's overall quality. Here are some good questions to ask:

*If you're buying a factory-configured system, does it have FCC
    certification? While it's not necessarily the case that a non-certified
    system is going to spew a lot of radio-frequency interference,
    certification is legally required ?? and becoming more important as clock
    frequencies climb. Lack of that sticker may indicate a fly-by-night
    vendor, or at least one in danger of being raided and shut down! (For
    further discussion, see the section on Radio Frequency Interference
    above.)
   
*Are the internal cable connectors keyed, so they can't be put in upside
    down? This doesn't matter if you'll never, ever ever need to upgrade or
    service your system. Otherwise, it's pretty important; and, vendors who
    fluff this detail may be quietly cutting other corners.
   

-----------------------------------------------------------------------------
10. Things to Check when Buying

10.1. Tricks and Traps in Warranties

Reading warranties is an art in itself. A few tips:

Beware the deadly modifier "manufacturer's" on a warranty; this means you
have to go back to the equipment's original manufacturer in case of problems
and can't get satisfaction from the mail-order house. Also, manufacturer's
warranties run from the date they ship; by the time the mail-order house
assembles and ships your system, it may have run out!

Watch for the equally deadly "We do not guarantee compatibility". This gotcha
on a component vendor's ad means you may not be able to return, say, a video
card that fails to work with your motherboard.

Another dangerous phrase is "We reserve the right to substitute equivalent
items". This means that instead of getting the high-quality name-brand parts
advertised in the configuration you just ordered, you may get those no-name
parts from Upper Baluchistan ?? theoretically equivalent according to the
spec sheets, but perhaps more likely to die the day after the warranty
expires. Substitution can be interpreted as "bait and switch", so most
vendors are scared of getting called on this. Very few will hold their
position if you press the matter.

Another red flag: "Only warranted in supported environments". This may mean
they won't honor a warranty on a non-Windows system at all, or it may mean
they'll insist on installing the Unix on disk themselves.

One absolute show-stopper is the phrase "All sales are final". This means you
have no options if a part doesn't work. Avoid any company with this policy.
-----------------------------------------------------------------------------

10.2. Special Questions to Ask Web/Mail-Order Vendors Before Buying

*Does the vendor have the part or system presently in stock? Mail order
    companies tend to run with very lean inventories; if they don't have your
    item in stock, delivery may take longer. Possibly much longer.
   
*Does the vendor pay for shipping? What's the delivery wait?
   
*If you need to return your system, is there a restocking fee? and will
    the vendor cover the return freight? Knowing the restocking fee can be
    particularly important, as they make keep you from getting real
    satisfaction on a bad major part. Avoid dealing with anyone who quotes
    more than a 15% restocking fee ?? and it's a good idea, if possible, to
    avoid any dealer who charges a restocking fee at all.
   

Warranties are tricky. There are companies whose warranties are invalidated
by opening the case. Some of those companies sell upgradeable systems, but
only authorized service centers can do upgrades without invalidating the
warranty. Sometimes a system is purchased with the warranty already
invalidated. There are vendors who buy minimal systems and upgrade them with
cheap RAM and/or disk drives. If the vendor is not an authorized service
center, the manufacturer's warranty is invalidated. The only recourse in case
of a problem is the vendor's warranty. So beware!
-----------------------------------------------------------------------------

10.3. Payment Method

It's a good idea to pay with AmEx or Visa or MasterCard; that way you can
stop payment if you get a lemon, and may benefit from a buyer-protection plan
using the credit card company's clout (not all cards offer buyer-protection
plans, and some that do have restrictions which may be applicable). However,
watch for phrases like "Credit card surcharges apply" or "All prices reflect
3% cash discount" which mean you're going to get socked extra if you pay by
card.

Note that many credit-card companies have clauses in their standard contracts
forbidding such surcharges. You can (and should) report such practices to
your credit-card issuer. If you already paid the surcharge, they will usually
see to it that it is returned to you. Credit-card companies will often stop
dealing with businesses that repeat such behavior.
-----------------------------------------------------------------------------

10.4. Which Clone Vendors to Talk To

10.4.1. Some pans

Gateway: may also be a vendor to avoid. Apparently their newer machines don't
have parity bits in their memories; memory is tested only on reboot. This is
dubious design even for Windows, and totally unacceptable for Unix.
-----------------------------------------------------------------------------

10.4.2. Some picks

In early August 2001 I designed an `Ultimate Linux Box' with Gary Sandine and
John Pearson of Los Alamos Computers; you can [http://www.catb.org/~esr/
writings/ultimate-linux-box/] read all about it These guys know what they are
doing and are fun to work with. If you need a high-end Linux workstation, or
your laboratory needs a computer cluster, talk with them.
-----------------------------------------------------------------------------

11. After You Take Delivery

Your configuration is custom and involves slightly unusual hardware.
Therefore, keep a copy of the configuration you wrote down, and check it
against the invoice and the actual delivered hardware. If there is a problem,
calling back your vendor right away will maximize your chances of getting the
matter settled quickly.
-----------------------------------------------------------------------------

12. Software to go with your hardware

I used to maintain an entire separate FAQ on Unixes for 386/486 and Pentium
hardware. Times change, industries evolve, and I can now replace that FAQ
with just three words:

Go get Linux!

Note FreeBSD or OpenSolaris are currently niche choices, but if they offer   
     something you need that Linux doesn't, don't let me stop you from trying
     one or both of them.                                                    
-----------------------------------------------------------------------------

13. Other Resources on Building Linux PCs

The [http://www.pctechguide.com/] PC Tech Guide offers pretty comprehensive
descriptions of PC hardware technologies.

The Caveat Emptor guide has an especially good section on evaluating monitor
specifications.

Anthony Olszewski's Assembling A PC is an excellent guide to the perplexed.
Not Linux-specific.

Tom's Hardware Guide covers many hardware issues exhaustively. It is
especially good about CPU chips and motherboards. Full of ads and
slow-loading graphics, though.

The System Optimization Site has many links to other worthwhile sites for
hardware buyers.

Christopher B. Browne has a page on [http://linuxfinances.info/info/
linuxvars.html#VARS] Linux VARs that build systems. He also recommends the 
Linux VAR HOWTO.

Jeff Moe has a Build Your Own PC page. It's more oriented towards building
from parts than this one. Less technical depth in most areas, but better
coverage of some including RAM, soundcards and motherboard installation.
Features nifty and helpful graphics, one of the better graphics-intensive
pages I've seen. However, the hardware-selection advice is out of date.

The Linux Hardware Database .

The Silent PC Reviews site has lots of good material on building quiet PCs.
