User Guide

2-10 Chapter 2
¯ Presentation and Installation of the CPU
Since 1996, every two or three months, Intel adds new models to the Pentium
CPU series. That is why the CPU market is filled with a lot of different models and
brands. All CPUs have different electrical specifications. That’s why installing a
CPU is becoming more and more complex. You can’t help that, because
everybody wants to be able to upgrade their hardware. So, you have to take a bit
of time to read this section, in order to be able to install a cheaper and better
processor.
The IT5A mainboard does not only support all the CPUs listed in the
specifications, but also has reserved several circuits in order to be able to support
future processors.
Related terminology :
External clock
Also referred to as the external CPU clock, or “Bus clock”, it is the input
clock of the CPU. For instance, Intel Pentium P90, P120 and P150 all have a
60MHz external CPU clock, but have different internal clock multiplier
factors.
Clock multiplier factor
The real operation clock within the CPU is the multiple of the external clock.
We refer to this factor as the clock multiplier factor. The four factors possible
are 1.5, 1.75, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5. The factor differs from one CPU to
another. For instance, the Intel Pentium 166 CPU has a 66MHz external
clock, with a multiplier factor of 2.5, so that the speed of the internal clock is
66MHz x 2.5.
Internal clock
Also referred to as the real internal CPU clock, it is the actual internal
operating clock of the CPU. The Internal Clock is a multiple of the external
clock and of the clock multiplier factor. For instance, the Intel Pentium 90
CPU has a 60MHz external clock and its clock multiplier factor is 1.5; the
Intel Pentium P133 CPU has a 66MHz external clock and its clock multiplier
factor is 2.
Internal CPU clock = clock multiplier factor * external CPU clock