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 documented HERE.
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.
Here's how a stock P90 card looks 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:
(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.
The blue patch wiring I added is visible in this wide shot:
Here's a 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.
Once the Overdrive is installed, the complex will look like this:
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.