This is a Type 4 P90 complex (as used on the Server 500 machines) upgrade that is still
somewhat not fully proven. Its exact origin is unknown. However, Aron Eisenpress
has relayed to the PS/2 community with the details on performing this mod, which is also
Be aware that there are some caveats to this mod that may discourage the uninitiated, especially the
need to actually add "patch" wiring to the processor socket on complex itself. If you are inclined
to do so though, the enhanced performance of a 180 MHz or 200 MHz MMX processor on a Micro Channel
machine may prove to to be intoxicating. This documentation will outline a conversion to the
Pentium 200 MMX Overdrive.
As with other Type 4 P90 complex mods, the conversion of the base-clock speed is optional. Whether
you chose to stick with the stock 60 MHz oscillator or upgrade to a 66 MHz unit is entirely up to you.
Stock P90 card without the heatsink
Between the processor and the cache controller is the oscillator, which in this case has replaced by
a faster 66.667 MHz unit.
66.667 MHz Oscillator
(Note: I've used both the 66 MHz and 66.667 MHz oscillators successfully.
However, if you feel the need for maximum compatibility and stability,
the 66 MHz unit as used on the Type 4 P66 complex might be the better choice)
Once the oscillator is replaced, the complex operates at 66 MHz, much like the Type 4 P66 complex.
The next thing that must be done to accommodate a Pentium 200 MMX Overdrive is add some wiring which
routes a 5V power source to the appropriate pins on the socket to drive the built-in heatsink/fan
unit that exists on the Overdrive. This wiring is done on the back side of the complex, on the
lower-right section of the board.
View of the patch wiring
Close-up view detailing the pins that need to be connected with the patch wire
With the patch wiring in place, the socket is now theoretically "overdrive-capable", and the complex
is ready to accept a Pentium 200 MMX Overdrive part.
Processor complex with the Overdrive processor installed
That's about it! The Pentium 200 MMX Overdrive fits very nicely onto the complex, with the
end-result performance gain being very noticeable. The only drawback is that there have been
some unexplained failures experienced under both NT and Windows that may or may not
be directly related to the modification. If you perform this mod, please update the
PS/2 newsgroup with your experiences.