Q During a recent upgrade from a 90MHz to 133MHz Pentium I was told that the speed display on the computer box could not be changed from 90. Yet later on, when looking inside the box for another reason, I saw lots of jumpers at the back of the speed display. This made me wonder whether the display can in fact be changed, if you know what you're doing, or is it a case of trial and error?

A To understand the nature of the speed display, you need to understand the function of the turbo button found on many computers. The turbo button changes the processorÆs clock speed between the normal high-speed setting and a lower speed setting. The question is often raised, why have a turbo button? Mostly it is for historical purposes. When IBM made its first PC, it ran with a clock speed of 4MHz. Their next model had a processor that ran at 8MHz. Unfortunately, expansion cards that had been made for the original 4MHz version were tied to that clock speed and could not operate at the increased speed. By including a turbo option you were able to slow down the processor of the computer so that it ran at 4MHz and then you could use the older expansion cards. Later models had expansion slots designed so that the cards could run at speeds independent of the processor.

So the turbo button is unneeded and many computers now donÆt even have one. However, game players have found one additional use for the turbo button. A lot of older games ran as fast as the processor did. Run a game designed for a 386 on a Pentium II and it will run so quickly that it is impossible to play. The turbo button can be used to slow things down to a more playable speed. Most new games are designed so that increases in processor speed wonÆt increase the speed of game play beyond the intended level.

Many computers have a light that is on for the normal (turbo) setting and off when the button is out. Some computers display "HI" and "LO" for the two settings. Your computer displays "90" and a lower number when the turbo setting is off. The number on the display bears no relation to the actual clock speed. The little device for displaying numbers obviously has some mechanism to set what number it displays, but it may be unable to display more than two digits. The first 100MHz computer I owned had a display like that, so the suppliers set it to display 99. If the display mechanism is not documented, you can safely engage in a process of trial and error. Your changes will not affect your computer.