73
3 System Board (P/Ns D3657-63001 and D3661-63001)
Devices on the Processor Local Bus
The computer will execute erratically, if at all, if the configuration switches
are set to operate at a higher processor speed than the processor is capable
of supporting. This may cause damage to the PC.
Setting the switches to operate at a slower speed than the processor is
capable of supporting would not cause any failure of operation but would
cause instructions to be executed more slowly than they should be.
Cache Memory
The PC allows for the provision of two levels of cache memory:
•
Level-one cache memory which is fabricated by Intel in the Pentium
processor chip
•
Level-two cache memory is optionally installed as a memory module on
the system board
Each acts as temporary storage for data and instructions from the main
memory. Since the system is likely to use the same data several times, it is
faster to get it from the on-chip level-one cache than from the main memory.
The level-two cache memory, when fitted, has a 32-byte line size (a line is an
area of memory of a fixed size). It is controlled by the PL/PCI bridge chip
(SB82437FX). A single HP cache memory module consists of 256 KB of
direct mapped, synchronous or asynchronous, static random access memory
(SRAM). The synchronous cache memory module achieves 10% better
performance than the asynchronous module.
1
2
Processor-
Local Bus
Frequency
3
4
7
Frequency
Ratio
(Processor:
Local Bus)
Processor
Frequency
Open
Closed
66 MHz
Closed
Closed
Closed
2.5
166 MHz
Closed
Open
60 MHz
Open
Closed
Closed
3.0
180 MHz
Open
Closed
66 MHz
Open
Closed
Closed
3.0
200 MHz
Switch
Switch
