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P5SD-B User’s Manual
3: Reconfiguring Your Mainboard – 3.10
Configuring External Clock Speed & Factor
To configure the board for a CPU’s internal clock speed, you
have to set the external clock speed (sometimes referred to as the
bus speed) and the clock factor so that the result is the internal
clock speed of the CPU you are installing. For example, the de-
fault setting for these is:
66.6MHZ [external clock] x 3.0 [clock factor] =199.8MHz
or, an effective setting of 200MHz.
Since the internal clock speed the CPU is supposed to operate
at is fixed, the two factors, external clock and clock factor, are the
variables. The CPU manufacturer or vendor’s information should
tell you what these factors should be.
P Rated CPUs
Cyrix, IBM and AMD all make Pentium ® -class CPUs that are
performance rated at an Intel Pentium ® equivalent speed but ac-
tually may have a slower internal clock speed. This ‘P’ rating is
used to indicate the CPU’s performance rather than its internal
clock speed. For example, the Cyrix/IBM P200 has an actual in-
ternal clock speed of 150MHz. If you install a CPU of this type,
make sure you set the mainboard for the actual internal clock
speed of the CPU, not its P rating.
Configuring CPU Voltage
The CPU voltage specification should also be provided in in-
formation from the manufacturer or vendor. Standard Pentium ®
CPUs are single voltage. MMX Pentiums ® are dual-voltage. You
should set the CPU Voltage jumpers according to the specifica-
tions you get with the CPU.