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[ The PC Guide | The PC Buyer's Guide | Designing and Specifying PC Systems and Components | Key Performance Issues In PC System Design ]

The Dangers of "Magic Numbers"

One of my biggest pet peeves about the way PC systems and components are advertised is the tremendous focus that companies place in their ads on what I call "magic numbers". They often try to boil down all the characteristics of a PC system to a few key figures; you'll end up seeing something like this: "Pentium III 833, 128 MB, 16 MB video, 10 GB hard drive, 17" monitor, 56K modem". There are people who will buy a system based on little more than this level of information.

Well, those numbers do tell you at least the basics of the system. You can tell at a glance what the fundamental characteristics of the system will be, and I would agree that you could use that amount of detail to rule out a system that clearly did not have what you wanted. But to go much beyond that with that little detail would be dangerous indeed, because there is far more not being said about the components in this system than actually is being said.

Take one component, the hard disk drive. It's 10 GB, fine, capacity is important, but that's not nearly enough information to let you decide if you want it or not! What's the model and what is its reliability level? How old is it? What's the spindle speed? How about the seek time specification? The density of the platters? How much noise does it make? What is the service life and MTBF of the drive? Who is the manufacturer and what is their support and warranty track record?

How about the monitor. 17" is the nominal size, but what's the viewable image size? Is it a flat screen? Anti-glare coating? Trinitron tube or not? What sorts of controls does it have? Dot pitch size? Maximum resolution? Refresh rate limits? And by far the most question: what does the monitor look like, how is it on the eyes?

Virtually every component has a "magic number", sometimes two or more, that PC system makers and sellers use to try to "distill" down the characteristics of that part of the system. In doing this, not only are they omitting almost all the key details about the quality and performance of the part, much of the time even the number they give you is worthless, or nearly so. These numbers are usually based in fact, but exaggerated. In some cases they have little bearing on overall performance at all.

To take the hard disk example again: some companies focus on the speed of the interface; they'll say "this drive uses UDMA/100, three times the speed of the old UDMA/33 standard!" In fact, the speed of the interface, 100 MB/s vs. 33 MB/s, makes a difference of only a few percentage points in the speed of the hard drive.

I really can't blame the manufacturers and vendors of components entirely for the attention given these "magic numbers". They know what sells, and they focus on it. The problem lies in part with consumers that look too much to capacity and performance and too little to the other important characteristics of the components in their systems. Of all the magic numbers tossed around, the three worst are the speed of the CPU, the size of the system memory, and the capacity of the hard disk drive. These are three very important attributes, but they are not sufficient information for assessing even their respective components, much less a whole PC.

Make sure that you always get full detail on all the components in any system you design or buy. Don't fall for the "magic number" trap. I discuss the magic numbers associated with each component in the section discussing tips for component specification. Use the buying tips there to guide your component evaluations.

Next: Using Review Resources Wisely: Avoiding "Benchmark Bogosity"

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