Devices On The Processor-Local Bus; The Intel Pentium Microprocessor - HP Net Vectra Technical Reference Manual

Processor Cooling
Bus Frequencies
2 System Board

Devices on the Processor-Local Bus

Devices on the Processor-Local Bus

The Intel Pentium Microprocessor

The Pentium processor is packaged in a pin-grid-array (PGA), and is
seated on the system board in a zero-insertion-force (ZIF) socket 7. Only
upgrades that are pin compatible with the original processor, manufactured
by Intel, are supported.
P54CS chips working at 166 and 200 MHz require between 3.45 and 3.60 V.
A VRE voltage regulator, integrated on the system board, actively derives
the voltage from the 3.3 V, 5 V and 0 V outlets of the power supply.
The processor is cooled by two heat-sinks: one on the processor (as
normal), the other beside the system board. Surplus heat is carried from the
first to the second by a heat pipe.
Since it involves no moving mechanical parts, it is unlikely to fail, and so
involves no new support strategy.
Any thermal contact material between the parts and the heat-sinks must not
be removed or disturbed. The cooling needs of the processor are critical.
The location of the system board switches is shown in the diagram on page
16. Five of these switches (SW-1,2,3,4 and 5) determine the working
frequencies of the PC, as summarized in the table below. The uses of the
other switches are summarized on page 31.
There is a 14.318 MHz crystal oscillator on the system board. This frequency
is multiplied to 66 MHz by a phase locked loop. This is further scaled by an
internal clock multiplier within the processor. For example, the 200 MHz
processor multiplies the 66 MHz system clock by three. Switches 1 and 2, on
the system board switch bank, set the frequency of the Processor-Local bus.
Switches 3, 4 and 5 set the clock multiplier ratio. The PCI bus works,
synchronously, at half the frequency of the PL bus. The ISA bus works,
synchronously, at a quarter of the frequency of the PCI bus.
You will need to change these switches if you exchange or replace the
system board during a repair, so as to match the speed to that of the
processor. You will not need to change the switches if you upgrade the
original processor using the correct Intel Overdrive. No other types of
processor upgrade are supported by HP.
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