17.1 Core Components

The discussion in this chapter focuses on desktop computers. With the exception of notebooks , I build my machines from components. The goal is not to save money; in fact, the finished system often costs more than similarly outfitted pre- assembled computers. The advantage is that there are fewer headaches with custom configurations. If you know exactly what goes into your computer, you will have no surprises, and in this territory, surprises only come in the unpleasant variety. You don't want hardware that Linux doesn't support, and an unreliable piece of hardware can seriously degrade your quality of life.

Assembling a computer is easy, but it isn't for everyone. It takes time and a certain amount of dexterity to avoid hurting yourself on sharp electronic pieces. If you don't want to go for an off-the-shelf model that may contain unknown components, and you also don't want to assemble your computer yourself, you still have two choices. You can find out exactly what is in that off-the-shelf model that you're looking at, and then determine whether the parts will work with Linux. Reputable manufacturers list this information and do not substitute parts. Your other choice is to buy custom parts and then have a small computer shop or friend assemble them for you. If you go to a shop, make it clear that component substitution is unacceptable.

You need the following components:

A motherboard. Modern motherboards have integrated hard drive interfaces, as well as USB and many other I/O ports.
A processor (CPU).
Random-access memory (RAM).
A hard disk.
An Ethernet NIC card (optional).
A graphics card.
A case to hold the components. The case usually includes a power supply.

17.1.1 Processor and Motherboard

Virtually all IA32-like (x86 PC) central processing unit (CPU) models work with Linux. The kernel and gcc compiler support many vendor-specific CPU optimizations, and features such as multiprocessing also work well with Linux.

Two important considerations when choosing a processor should be power consumption and heat. CPUs that consume more power also generate a substantial amount of heat. To handle the extra heat, you need a lot of fans. Never overclock a processor running Linux , unless you like to see your computer crash.

Note

If you are interested in taming the usual din that a computer makes, a great place to start is the power supply. Most power supply units included with PC cases are of the very cheapest sort , with loud, unreliable cooling fans. You can easily replace the power supply with a low-noise premium model from a third party. It will not be cheap, but if noise irritates you, it is worth every penny.

Although nearly all CPU models will work with Linux, some care must be taken when choosing the CPU's home ” the motherboard. You should consider your motherboard, processor, and memory as a single unit, and you may even want to choose your motherboard first and find a CPU to fit. After all, it is possible that your motherboard will cost more than the CPU!

Pick a motherboard that has been available for a reasonable amount of time. Three or four months should be sufficient. Often, initial releases of motherboards have bugs that cause mysterious hardware failures. Avoid fancy (untested) new features. Linux doesn't immediately support each new bell and whistle that comes off the assembly line, and these unusual features may interfere with normal system operation. Watch out for brand-new processor models that require you to purchase a new motherboard chipset, as these can be expensive nightmares.

Modern motherboards come with a number of integrated peripherals. They normally include two ATA disk interfaces, plus parallel, serial, and USB ports. Some motherboards come with additional hardware, such as integrated SCSI controllers, video chips, and sound. These integrated features can save you space on the motherboard and the hassle of installing your own components, but if you buy separate plug-in components, you can perhaps save a little money and a compatibility headache . The advantages of integrated motherboard components are somewhat dubious in the case of most components except SCSI controllers. If, like many people, you choose a motherboard with integrated video, find out what chip it uses and make certain that the XFree86 server has support for it (see http://www.xfree86.org/ and http://www.xouvert.org/).

17.1.2 Memory

The third guideline from the beginning of this chapter ("you often get what you pay for") is most important when buying memory. Name -brand memory is only marginally more expensive than generic labels, and it can save you many headaches. A Linux machine exhibits odd behavior if it has bad memory. If a program seems to crash often, look for these symptoms:

The crash happens in the same place every time.
Rebooting makes the problem go away.
The operating system appears unaffected, and other programs run fine.
It happens during frequent disk access.

You should consider buying ECC (error-correcting code) memory. It is a little more expensive than standard memory, and not all motherboards support it (read your motherboard manual carefully ), but ECC memory practically ensures that you never have a memory problem.

A Linux system automatically uses extra memory for disk cache, and this can substantially improve performance for applications that use large files (or several small files). However, for many users, there is a point where more memory adds little or no benefit because the system has already cached nearly everything. You can briefly check the state of a system's memory utilization with the free command; the information in /proc/meminfo has a little more detail.

17.1.3 Hard Disk

The old "IDE versus SCSI" question was once one of the bigger debates surrounding hard disks. However, if you want to build a desktop computer, the debate means little, because you will likely choose an ATA (IDE) disk out of cost concerns. In the old days, power users considered ATA disks to be performance dogs, and there wasn't a large disparity in price when compared against SCSI disks. Improvements in CPU speeds, caching, memory cost, the interface, and hard disk manufacturing techniques have made ATA perform tolerably well for a desktop system with a single disk ” even Apple switched its desktop disks to the ATA type.

A disk has two primary specification numbers : average access time (measured in milliseconds , or ms) and rotation speed (measured in rotations per minute, or RPM). In general, a faster (lower) access time is the more important consideration for Unix, because the system spends a lot of time looking at a bunch of small files. If you are a software developer, this is particularly important because compilers and scripting languages use many file accesses on a single invocation. On the other hand, if you have big files (movies, music, whatever), a higher rotational speed gets this stuff off the hard disk faster.

There usually isn't a trade-off between rotational speed and access time because they are linked. More RPMs mean that the disk head takes less time to pass over the proper place on the disk platter for the next access, hence a lower average access time.

Higher performance, however, comes at a price above and beyond the sticker price. The fastest -spinning disks are usually noisy and generate more heat. I'll spare you the "hard disks I have hated in the past" war stories, but if you want a quiet disk, look for one with a fluid bearing system (sometimes called FDB). These drives use liquid instead of solid ball bearings for their platters, and they are a big improvement for your ears.

Any ATA disk should work in a Linux system. The kernel disk drivers are fast, and they support special features with the hdparm command. If you run into compatibility issues, they will likely be between your motherboard and the disk (in particular, some older motherboards do not support disks larger than 32GB; look for jumpers on the disk to "clip" the disk, limiting it to a lower capacity).

If you put two ATA disks in the same system, put them on different interfaces (your motherboard should have primary and secondary ATA interfaces), which should improve concurrent access slightly. If you purchase an add-in ATA interface card, you may need extra drivers. When considering one of these cards, look for drivers in the ATA support menu described in Section 10.4.1.

17.1.4 Network Cards and Infrastructure

The Linux kernel supports most wired PC Ethernet devices (also known as NICs, or network interface cards), but you should check any card against the compatibility list in a current Linux kernel. Don't believe a manufacturer's claim of compatibility in this case ” the manufacturer may require you to install a special kernel driver before the device works. Keep in mind that the kernel drivers that come from vendors often don't work correctly.

Most cable and DSL adapters require an Ethernet card. You should be able to use any supported Ethernet card regardless of the protocol that you use, provided that Linux supports the protocol. You may need to use a funny protocol like PPPoE for your provider (see Section 5.9).

Current networks of 100Base-T (100 megabits per second, or about 12 megabytes per second) are more than adequate for most purposes. They are also very inexpensive. To attach several machines to a home network, you need a hub or switch (it is possible to connect two machines directly with an Ethernet crossover cable, but this isn't really worth the trouble).

The most significant differences between using a hub and a low-end switch is that a switch can send and receive signals at the same time and therefore has a potential of faster throughput and lower latency. However, unless you have a habit of sending large files around your network simultaneously , you won't notice much of a performance difference between the two. On the other hand, the difference in price between hubs and switches is also fairly small. Whether you purchase a hub or a switch, pick a model that has ports for each of your computers, plus a few extra. Also, make sure that the hardware supports the older 10Base-T standard. This feature is often called 10/100 , and it provides the most convenient way to move files from an old computer with a 10Base-T interface.

Wireless Ethernet

You may want to consider wireless Ethernet for a notebook, even if you don't plan to use Ethernet when you're on the go. There are several advantages:

It is one less cable to connect. This saves time as well as wear and tear on the machine.
Visitors with wireless cards can connect to your network without much hassle.
Some PDAs can connect to a network with wireless Ethernet.
You may need to connect to a foreign network at some time.

There are also some disadvantages:

It is more expensive.
Security can be a hassle (see Section 5.15.1).
There are some really annoying twerps who think that wireless Ethernet makes them the coolest people on the planet.

To make wireless Ethernet work, you need a wireless access point along with the network card (some notebooks come with integrated cards). Many access points come in units that also provide a broadband router and an integrated switch. Even if you don't have a broadband connection or choose not to use the routing feature, the switch can still be useful for connecting desktop computers.

For notebook Ethernet cards, see Section 11.6. For information on how to set up a wireless client, see Section 5.15.

17.1.5 Graphics Hardware

Your primary concern in choosing a video card should be compatibility with XFree86. Although you can inspect the list of compatible cards at http://www.xfree86.org/ and http://www.xouvert.org/, it is unfortunately not always easy to identify a card because manufacturers have a habit of not changing product names while altering hardware significantly.

As with the motherboard, a good method for ensuring that your graphics hardware is compatible with your system is to identify a brand or particular graphics chip that has consistent support and then find a video card that isn't cutting-edge. If a card has been available for some time, there is a much greater chance of XFree86 support. Regarding performance, quick video hardware often means very little under Linux; in fact, the fastest 3-D hardware may not be optimal for normal tasks in XFree86.

XFree86 supports multi-output video cards and additional cards that can drive multiple monitors , sometimes called multiple heads . If you value your onscreen workspace, this is worth looking at because the emergence of LCD displays makes it feasible to have two large monitors without a desk the size of an aircraft carrier. You can also combine multiple displays into one big virtual display with the Xinerama extension.