THE SITUATION 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 very nicely documented on Louis' site. 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 180MHz or 200MHz MMX processor on a Micro Channel machine may prove to to be intoxicating. This documentation will outline a conversion to the Pentium 200MMX Overdrive.

THE SOLUTION 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 60MHz oscillator or upgrade to a 66MHz 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 66.667MHz unit: (Note: I've used both the 66MHz and 66.667MHz oscillators successfully. However, if you feel the need for maximum compatibility and stability, the 66MHz unit as used on the type-4 P66 complex might be the better choice) Once the oscillator is replaced, the complex operates at 66MHz, much like the Type-4 P66 complex. The next thing that must be done to accomodate a Pentium 200MMX 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 200MMX Overdrive part. Once the Overdrive is installed, the complex will look like this: That's about it! The Pentium 200MMX Overdrive fits very nicely onto the complex, with the end-result performance gain being very noticable. 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. Disclaimer: As with all other contents on this site describing modifications that may boost the performance of your hardware, the author(s) are only describing methods that are for the most part "experimental" in nature. Some of these modifications will void your manufacturers' warrantee, and at worst may also permanently damage your hardware. If you choose to perform any of these modifications, please do so understanding these risks, as the author(s) cannot be held liable for any loss or damage that may result.