The Type 4 P90 complex (as used on the Server 500 machines) is currently the hot ticket
in PS/2 performance upgrades. Several different types of modifications have been
reported on the newsgroup as being successful, including the one detailed here. This specific modification
has been done by myself (Terminaut) on a number of complexes with much success.
Modifying the P90 complex to run a P200 requires two steps, the first of which isn't really
for the faint of heart since it requires that the 60 MHz oscillator on the precious P90 complex
be desoldered and replaced with a 66 MHz unit. I must admit that I shed some sweat
the first time I did this, but rest assured that it's not *all* that difficult to do if you have
the appropriate tools and a steady hand.
Stock P90 card without the heatsink
Between the processor and the cache controller is the oscillator, which gets
replaced by this faster 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 is to adjust the clocking-multiplier to be 3x. On the current
crop of clone motherboards this task is trivial, but since IBM's P90 complex doesn't have any
provision for adjusting such things, a workaround must be made. I did so by using an
"open" PGA 321-pin socket that has the appropriate pins connected via tiny wires soldered in place.
Louis has coined this item as the Terminauter, and I will refer to it as such hereafter.
Here are some shots of how the socket looks:
321-pin open-PGA socket modified for 3x Pentium clocking
The way the Terminauter works is by sitting in between the processor and the
processor complex itself. Since the appropriate pins have been hardwired to 3X on the Terminauter,
any Pentium processor that is mounted on it gets clocked at 3 times the base clock (in this case 66 MHz)
which yields 200 MHz.
P90 Complex looks with a P200 processor mounted on the Terminauter
As you might guess, the Terminauter unit incurs a slight height penalty on the processor, which
will cause a bit of difficulty when you try to mount the stock heatsink back in place. I bypassed
this problem by using a nice heatsink unit from a spare processor card off my Server 720 machine.
Full view of the completed P200 Type 4 complex
Close-up of the mounted Terminauter
That's about it! This particular setup has been running Windows NT-4 (with RAID) flawlessly for me.