Fundamentals - Designing a small PC
(Page 5 of 14 )
At the beginning of the millennium, some forward-thinking PC builders and manufacturers began to design and build PCs that were smaller and/or more portable than traditional mini-tower systems. Small PCs have become extremely popular, and it’s no wonder. These systems are small, light, easily portable, and fit just about anywhere. In order of decreasing size, small/ portable PCs fall into four broad categories:
LAN Party PC
A LAN Party PC is essentially a standard ATX mini- or mid-tower system with a handle and other modifications to increase portability, port accessibility, and other factors important in a “totable” PC. Most LAN Party cases are constructed largely of aluminum to minimize weight and maximize cooling efficiency. LAN Party PCs are often “trickedout” with colorful motherboards, clear side panels, fluorescent lights, fans, and cables, and other visual enhancements. Despite the customizations, LAN Party PCs are based on industry-standard components and are as capable as any standard PC. Chapter 5 describes the issues involved in designing and building such a system.
microATX PC
A microATX PC is basically a cut-down version of a standard ATX PC. The microATX case and motherboard are smaller and provide less expandability, but are otherwise comparable in features and functionality to a standard ATX system. The great advantage of microATX PCs relative to the smaller styles described below is that microATX PCs use industry-standard components. microATX cases are available in two styles. Slimline cases are about the size and shape of a VCR. “Cube” cases are typically 8" tall and roughly a foot wide and deep. The relatively small case capacity makes cooling more difficult and puts some restraints on the number and type of hard drives, expansion cards, and other peripherals you can install, but it is possible to build a reliable, high-performance PC in the microATX form factor.
Small Form Factor (SFF) PC
Small Form Factor (SFF) means different things to different people. We use the term here to mean the cube-style form factor pioneered by Shuttle ( http://us.shuttle.com) with their XPC models. (In fact, Shuttle says that SFF stands for Shuttle Form Factor.) Other companies, including Soltek, Biostar, and others, now produce cube-style SFF systems as well. These true SFF systems use proprietary cases, power supplies, I/ O templates, and motherboards, which limits their flexibility. In effect, “building” an SFF system consists of buying a “barebones” system with case, power supply, and motherboard, and adding your choice of memory, drives, video adapter, and so on. SFF PCs are typically more expensive, slower, and less reliable than standard size or microATX PCs, but they are noticeably smaller.
The limited space available in cube-style SFF cases restricts component choice. For example, you may have to purchase special low-profile memory modules, and you may not be able to install full-length, standard-height expansion cards. The tiny case volume also makes heat dissipation critical. For example, you may not be able to use the fastest available processors because the case is not capable of cooling them sufficiently.
Mini-ITX PC
Mini-ITX is a semi-proprietary form factor pioneered by VIA Technologies. Although a few minor third-party manufacturers supply Mini-ITX components, VIA products dominate the Mini-ITX market. Mini-ITX motherboards are 170mm (6.7") square, and are in effect smaller versions of microATX motherboards. Although Mini-ITX motherboards are available that accept Socket 370 Pentium III and even Socket 478 Pentium 4 processors, the majority of Mini-ITX systems use VIA motherboards with embedded processors. These processors are very slow relative to modern AMD and Intel processors, and Mini-ITX motherboards are relatively expensive. Even so, Mini-ITX has its place, for systems that do not require high performance but that need to be small and very quiet. Mini-ITX motherboards are so small that they can be built into enclosures as small as a cigar box (literally!), and the flip side to low processor performance is that these processors consume little power and produce little heat. Most Mini-ITX systems use passive cooling and “wall-wart” power supplies, which eliminates fan noise and allows the system to be almost totally silent. Mini-ITX is most appropriate for such “appliance” applications as small Linux servers, routers, and satellite DVR playback-only systems.
Table 1-1 lists the characteristics of each of these system types relative to a standard mini/mid-tower desktop system, using the rankings of Excellent (E), Very Good (VG), Good (G), Fair (F), and Poor (P).
| Desktop | LAN Party | microATX | SFF | Mini-ITX |
| Typical case volume (liters) | 35 to 60 | 25 to 40 | 12 to 20 | 8 to 12 | 2.5 to 9 |
| Size | P to F | F to G | G to VG | VG to E | E |
| Cost Efficiency | E | VG | E | P to F | P to F |
| Reliability | E | F to VG | VG to E | F to VG | F to VG |
| Portability | P | VG to E | F to VG | VG to E | VG to E |
| Noise level | VG to E | F to VG | VG to E | P to VG | E |
| Cooling | E | G to E | G to VG | P to F | F to E |
| Upgradability / Expandability | E | VG to E | F to VG | F to G | P |
| Processor performance | E | E | VG to E | VG to E | P |
| Graphics performance | E | E | VG to E | F to E | P |
| Disk Capacity / Performance | E | E | G to VG | G to VG | P |
Table 1-1. Small systems strengths and weaknesses
Table 1-1 presents best-case scenarios for each of the form factors. For example, not all standard desktop systems have excellent performance, nor are all of them extremely quiet. Rather, this table presents the best that can be done within the limitations of each form factor, which may vary according to the specific components you select.
If you need to design a small PC, recognize that each step down from standard mini-tower size involves additional compromises in performance, cost, reliability, noise level, and other key criteria. Reducing case size limits the number and type of components you can install and makes it more difficult to cool the system effectively. It also makes it harder to quiet the PC. For example, small cases often use relatively loud power supplies, and because the power supply is proprietary, installing an aftermarket quiet power supply is not an option. Similarly, using a small case forces you to trade off performance against cooling against noise. For example, you may be forced to use a slower processor than you’d like because the necessary CPU cooler for a faster processor is too large to fit in the available space or is louder than acceptable.
When it comes to designing small PCs, our rule is to use a standard mini-tower system whenever possible. If that’s too large, step down to a micro-ATX system. And if that’s too large, we suggest you rethink your priorities. Perhaps you could free some additional space by moving things around, or perhaps you could place the PC in a different position. Try hard to avoid using any form factor smaller than microATX.
Then—if and only if you are certain that the tradeoffs are worth it—buy a barebones SFF system and build it out to meet your requirements. We don’t think of Mini-ITX systems as direct competitors to traditional PCs at all; they’re simply too slow to be taken seriously as a mainstream PC. Instead, we suggest you consider Mini-ITX systems to be special, relatively expensive, low-performance computing appliances that are suitable only for very specialized applications.
 This chapter is from Building the Perfect PC by Robert Bruce Thompson and Barbara Fritchman Thompson (O'Reilly, 2004, ISBN: 0596006632). Check it out at your favorite bookstore today. Buy this book now.
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