Q: Why do the speeds of processor...

Q: Why do the speeds of processor chips in personal computers all come in multiples of 33 megahertz?

A: Not all processor chips come in multiples of 33. Primarily, those made by Intel Corp. do, but some made by other companies come in multiples of 25.

The key to the question is the speed of the bus or motherboard circuit that links all the major components of the computer, such as the mouse, modem, keyboard, etc., to the processor, according to Jag Bolaria of Intel. It is much easier and cheaper to build computers when the processor and the bus are operating at the same speed or at even multiples. So-called asynchronous computers, in which they do not, are more expensive to build and more difficult to test, he said.

The 33 MHz speed is a legacy from IBM. The first personal computers IBM built had a bus that operated at 8.333 MHz. Later, the speed was upped to 33.333 MHz, four times the original speed. Buses now operate at 66.666 MHz, and Intel will bring out a new one later this year that runs at 100 MHz.