P90 Tuning Logo
MCA Mafia Logo


[-1-]  Precautions and Warnings before you start !

[-2-]   Introduction to Type-4 Pentium 90 Platform

[-3-]   The importance of cooling certain components

[-4-]   Modification A) Using a Pentium Overdrive 180 / 200

[-5-]   Modification B) Hardwired BF0 / BF1 Pins for different Bus / Core ratio

[-6-]   Modification C) Altering the base-clock from 60 to 66MHz

[-7-]   Modification D) Using a MMX Interposer and P-233MMX CPU

[-8-]   Problems, Workarounds and other stuff

Visiting the MCA Enthusiasts Page

Introduction to Type-4 Pentium 90 Platform
Location of the important components

The IBM Type 4 P-90 Platform is also often referenced as the "Y-Platform" - because it showed up in the few Mod. 9595-xYx machines. Originally it came with the Server 500 and was offered as an option to the Model 95 series.
Preferably it is combined with the 95A planar, which can be identified by the two serial and two parallel ports and which offers optimum performance and support for all the platform features.

IBM Type 4 Platform with Pentium 90
IBM Type 4 Platform with Pentium 90

The codename of the platform was "Cubrun" (rumour says it were a small river), the IBM numbers brought in connection with it are
P/N 06H8589, FRU 06H7095 (with flawless P90)
P/N 06H3729, FRU 06H3739 (with buggy P90)
The latter one is the original P/N for FCC application. Earlier P/Ns may still have a buggy Pentium 90 processor installed. Intel had them replaced on demand.

No problem if you plan to replace that P90 against something else anyway.

The Type-4 platforms have 128KB IBM SurePath Flash-ROM based BIOS and offer a Synchro-Stream Mode for 40MB/s data transfer rates (up to 80MB/s in 64-bit burst transfers).

This platform is a so-called "Socket-5" board. The CPU connector is LIF (Low Insertation Force) but not ZIF (Zero Insertation Force) like the Socket 7. The socket layout is staggered in contrast to the older Pentium P60 and 66 and the 486 Type-4 platforms.

It uses the Intel Pentium 90 processor on a 2:3 bus/core ratio with a base clock of 60 MHz.
The Pentium-90 processor is accompanied by an Intel 82497-60 Cache Controller and a set of 10 Intel 82492-60 Cache RAMs for a total of 256K Level-2 Cache, 5 chips on either side of the card.
If you are lucky and got one of the platforms used on the last series of the IBM PS/2 Server 500, you may have 66 MHz rated cache RAMs and 82497 cache controller installed. However: the oscillator on these is still a 60.0000 MHz type and the platform runs on a 60 MHz base clock too.

Never ever install an 82496 cache controller from a P60 or P66 platform !

Not even for testing. It may even appear to work - but surely not for long. The controller used on the P60 platform is a 5V-only type, the one on the P90 platform is a "dual-plane" 3.3V / 5V chip. The P60 controller will short the 3.3V supply against the 5V and destroy cache RAMs and CPU.

The P90 platform also has one on-card voltage regulator for some of the other logic chips (LT1085, 3 Amps, set to 3.75V) and another voltage regulator for the Pentium 90 processor, the cache controller and the cache RAMs (LT1084, 5 Amps, set to 3.3V).

Back up to the Top

Return to the Previous Page
Flip over to the Next Page