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2 System Board
Devices on the Processor-Local Bus
Bus Frequencies
The location of the system board switches is shown in the diagram on page
20. Five of these switches (SW-1,2,3,4 and 7) determine the working
frequencies of the PC, and the three frequency multipliers (M1, M2 and M3),
as summarized in the table below. The uses of the other switches are
summarized on page 39.
There is a 14.318 MHz crystal oscillator on the system board whose
frequency is multiplied, by a phase locked loop, to 50, 60 or 66 MHz for the
Processor Local (PL) bus, according to the settings of SW-1 and SW-2. This
is further multiplied, to the processor core frequency, by a factor of 1.5, 2,
2.5 or 3, according to the settings of SW-3 and SW-4. The PCI bus works at
half the frequency of the PL bus. The ISA bus works at a third or a quarter of
the frequency of the PCI bus, according to the setting of SW-7.
You will need to change these switches when you replace the original system
board, for a repair, so as to match the processor. You will not need to change
the switches if you upgrade the original processor using the correct Intel
Overdrive. It is not recommended to upgrade to another processor that may
have different voltage requirements.
The computer may execute erratically, if at all, or may overheat, if it is
configured to operate at a higher processor speed than the processor is
capable of supporting. This can cause damage to the computer.
1.
Where there is a choice indicated, install the one that is appropriate for the given processor.
2.
These processors are not available for these models of HP Vectra PC at the time of printing. This
information is provided for completeness only.
Processor
Frequency
M1
PL Bus
Frequency
M2
PCI Bus
Frequency
M3
ISA Bus
Frequency
PL Frequency Multiplier M1 M3
VRM
1
SW-1 SW-2 SW-8 SW-3 SW-4 SW-7
75 MHz
2
1.5 50 MHz 2 25 MHz 3 8.33 MHz
Closed Closed Closed Open
Open Open
Vcc
90 MHz
2
1.5 60 MHz 2 30 MHz 4 7.5 MHz
Closed Open Closed Open Open Closed
Vcc
100 MHz
2
1.5 66 MHz 2 33 MHz 4 8.25 MHz
Open Closed Closed Open Open Closed
Vcc
120 MHz
2
2 60 MHz 2 30 MHz 4 7.5 MHz
Closed Open Closed Closed Open Closed
Vcc,Vre
133 MHz 2 66 MHz 2 33 MHz 4 8.25 MHz
Open Closed Closed
Closed Open Closed
Vcc
150 MHz 2.5 60 MHz 2 30 MHz 4 7.5 MHz
Closed Open Closed Closed Closed Closed
Vcc,Vmmx
166 MHz 2.5 66 MHz 2 33 MHz 4 8.25 MHz
Open Closed Closed Closed
Closed Closed
Vre,Vmmx
200 MHz 3 66 MHz 2 33 MHz 4 8.25 MHz
Open Closed Closed Open
Closed Closed
Vre,Vmmx
233 MHz
2
3.5 66 MHz 2 33 MHz 4 8.25 MHz
Open Closed Open Open Open Closed
Vmmx