The Bus Speed Guide

The Importance Of The Bus Speed

First of all, I think I should explain to all those who are unsure what 'Bus Speed' means and what it does.

The 'Bus Speed' is the frequency a Pentium, Pentium Pro, or compatible is tacted with externally. Only in the first days of the Pentium did the CPU run with the same tact/speed externally as internally. These were the days of the P60 and P66. A Pentium 60 was clocked at 60 MHz from the motherboard and its core was running at the very same speed. Times were changing and faster CPUs were needed, so Intel came out with the P90 and P100. These two fellows were still running at 60/66 MHz externally, but the core was multiplied by a factor of 1.5, which made a 90/100 MHz CPU. A short while later, Intel released the P75 to replace the P60 and P66. The P75 also runs with a multiplied speed: 50 MHz x 1.5 = 75 MHz. You know what has happened from there. Now we have the current Pentium flagship, which runs at 66 MHz externally and 200 MHz (66x3) internally.

So what does this 'runs externally' mean?

To start with, the external clock is obviously supplied by the motherboard. At this speed/frequency/tact the CPU is communicating with all of the system components that it's directly connected to. These are

• the Chipset
• the Ram
• the Second Level Cache

The chipset speaks to the PCI bus at exactly HALF the speed/frequency/tact, so that the CPU talks to all PCI devices through the chipset with HALF the external tact or bus speed.

Now, what do we know about the important performance components of a PC system?

• the CPU - well, that's covered, it's specified by it's clock speed
• the Second Level Cache - aha, determined by type, size and ... the bus speed
• the RAM - aha again, determined by the type, the size, the timing and ... the bus speed
• the Video Card - ugh, determined by the type and the PCI speed ... = bus speed/2
• the Harddisk(s) - allright, determined by the type, the bus type and of course the PCI Speed ... hence the bus speed

Well, it seems there's nothing in that box, which isn't influenced by the bus speed, so learn: TAKE GOOD CARE OF IT !!!