In personal computers, as with most other manufactured commodities, you can tell a lot about the culture of the age by studying the fancy names that manufacturers give their products. Five years or so ago, when the personal computer was still a fairly exotic new product, the rage in computer names was for high-tech connotations, for alpha-numeric combinations conveying a futuristic, Star Trek aura: Hence the "PC-XT," the "1000-SX," the "Digitron 64-S," and so on.

Today the word association experts in computer makers' new-name laboratories are burning to come up with monickers that suggest raw, unmitigated speed. So many new personal computers have the word "Turbo" in their names that you could almost believe the federal government had passed a law requiring it. Then there's the "Fox," the "Cheetah," and the "Lightning."

The prize winner, though, in the high-speed name sweepstakes is the PC sold under the label "TGV." Clearly the maker believes that its customers are such sophisticated world travelers they will all know the famous French passenger train called the "Tres Grand Vitesse," or "TGV," which hurtles through the central provinces at 250 or so kilometers per hour.

Computer makers are convinced that speed sparks sales, so they're assiduously selling speed. But all those ads and promises -- "Twice as fast as an XT!" -- can pose some traps for a buyer.

For one thing, many factors determine how fast a personal computer completes a particular task; thus, the speedy feature that a manufacturer touts in his ads may provide no benefit at all for the work you do on a computer. For another, it's not always clear that higher speed justifies a higher price. Let's say, for example, that your major work on a computer involves relatively small, simple spreadsheets that take five seconds to calculate. If you go out and buy a new "Super-Turbo" computer that runs twice as fast, you'll be saving all of 2.5 seconds each time you run the spreadsheet -- hardly worth a major expenditure.

Most of the advertisements pushing high-speed personal computers focus on the machines' "clock speed." This is the computer's basic internal rhythm, the standard metronome that sets the beat for every operation in the computer's central processing unit. Clock speed is usually measured in megaHertz, or MHz, with one MHz standing for 1 million operations per second. It's not easy, to say the least, for humans to contemplate something happening a million times per second. A clock beating at that rate will tick a few hundred thousand times in the interval it takes you to blink an eye. But all personal computers are built around processors that beat much faster than a million times per second.

To some extent, clock speed is a valid measure of a computer's working speed. It's only logical that a computer running at, say, 7.14 MHz will complete work faster than one running at 4.77 MHz. (As you may have guessed, these are not just random figures. The standard IBM-PC runs at 4.77 MHz; many "Turbo" computers have a microprocessor that can run at 7.14 MHz.)

In practice, though, clock speed isn't everything. Many other factors control a computer's rate of calculation: the microprocessor, the presence or absence of a "coprocessor" chip for heavy number crunching, the design of the machine's display system, the disk drive performance, and the speed of the memory chips. Consequently, a PC equipped with a 7.14 MHz microprocessor and two floppy disk drives (a common configuration for various "Turbo" MS-DOS clones on the market) will be slower on many jobs than a 4.77 MHz machine that has a fast hard disk installed.

Let's assume, though, that you purchase an incredibly souped-up PC that is built for speed in every dimension: the clock speed, the memory access, the disk drives, etc. How much difference will "grand vitesse" performance make for the average computer user? I've been contemplating that question recently while test driving one of the fastest personal computers on the market: the 12 MHz Compaq Portable III. In a couple of weeks, I'll give you the answer in this space.