P90 Platform Tuning

Table of Contents

[-0-]  Version History, Disclaimer & Legal Info
[-1-]  Precautions and Warnings before you start
[-2-]  Introduction to the Type 4 "Y" Pentium 90 Platform
[-3-]  The importance of cooling certain components
[-4-]  Modification A) Using a Pentium Overdrive 180 / 200
[-5-]  Modification B) Hardwiring the BF0 / BF1 Pins for different Bus / Core ratios
[-6-]  Modification C) Changing the Base Clock from 60 to 66 MHz
[-7-]  Modification D) Using a Pentium MMX 233 MHz with an Interposer
[-8-]  Problems, Workarounds and other stuff

Content by Peter H. Wendt (original HERE). Modified by Major Tom.

Precautions and Warnings before you start

  1. The complex is sensitive to electrostatic discharge (ESD). You should make sure that your workplace has a conductive or static dissipative surface that is properly grounded to avoid build-up of static charge. If you don't have appropriate working surface, at least discharge yourself by touching some grounded metal object. Try to do this regularly when working on the board (before you touch it!). Static discharge may destroy or degrade the ESD sensitive ICs and/or other components.

  2. You will need a soldering iron with a fine tip, and ideally with some kind of temperature control. None of the modifications that require soldering operations are of high complexity or over-average difficulty range (Except where otherwise noted). But you will need some basic soldering skills and steady hands.

  3. Think again about the value and rarity of the "Y" complex. If you don't feel confident about your skills and are a bit worried remembering how much care and money it may cost to get another "Y" board... just don't risk it. Be happy with what you have or try to get somebody more experienced to do the work for you.
    Most of the modifications are easily reversible, for the sake of all the purists out there.

  4. And once again - you are doing this at your own risk. The author is not responsible for any damages or losses. Or in simple words - if you fudge it up, it's your problem!

A few words about the platform BIOS

The last BIOS for the Type 4 platform was Revision 10. It was designed to solve some time/date problems for machines running OS/2. This version however has some downsides with faster processors. It works fine with e.g. a 120 MHz clocked CPU (a P-133 set to 1:2 bus/core ratio at 60 MHz base clock) but faster combinations often fail with error 0129 xxxx. I don't know exactly what BIOS change caused this misbehaviour, but it's a known fact. Obviously the Revision 10 alters some settings for the cache controller that are not really well thought out (see comments below).

Therefore I would suggest to stick with BIOS revision 08, which had proved to run reliably with the Pentium Overdrive 200 (PODP200) as well as with a souped-up platform with the "Classic Pentium" 200 or even a MMX interposer and Pentium MMX running at 180 MHz with the original 60 MHz base clock.

Ed. Tom: The rev. 09 and 10 image doesn't contain any code changes that could affect the platform stability. All processor complex registers are programmed the same way.

More info about the different BIOS revisions can be found HERE.

233 MHz with a modified 66 MHz base clock is difficult. The system crashes with cache or processor board errors from the 0129 xxxx range. This is most likely caused by some timing issues...

Important: BIOS update is a fairly sensitive and risky process, so I would recommend to upgrade/downgrade the platform BIOS to Revision 08 BEFORE any processor or clock rate changes are made. Particularly altering the clock from 60 to 66 MHz might be quite hard to digest for the board, and it may cause instability. You don't want the system to crash during the flash update process...

Failed flash update may render the complex non-functional!

Ed. Tom: Normally this shouldn't happen as the flash chips are updated one at the time, and in a way where the system always has at least one functional copy of the Stage 1 POST code available to it. If the update process gets interrupted you may have to move the bank selection jumper to the other position to make the system POST in a flash-recovery mode. More information HERE.) However if that doesn't work for some reason, there is no other easy way to recover the BIOS. The flash chips are soldered and cannot be easily removed for reflashing in a programmer. Not without a rework station anyway.

Content created and/or collected by:
Louis Ohland, Peter Wendt, William Walsh, David Beem, Tatsuo Sunagawa, Jim Shorney, Tim Clarke, Kevin Bowling, Tomáš Slavotínek, and many others.

Ardent Tool of Capitalism - MAD Edition! is maintained by Tomáš Slavotínek.
Last update: 13 Sep 2021 - Changes & Credits | Legal Info & Contact