You can always underclock your P166MMX to 75 MHz.

since you have other systems as well speed issues are of no concern - so keep the 233mmx as-is. I use one as well for almost all my DOS needs , ICACHE does wonders to make it behave like a 386DX40 and 3D FPS games love 233mhz

GPA wrote:

You can always underclock your P166MMX to 75 MHz.

Nope. Minimum 2x multi and I've never seen a board capable of less than 50mhz fsb.

gdjacobs wrote:

GPA wrote:

You can always underclock your P166MMX to 75 MHz.

Nope. Minimum 2x multi and I've never seen a board capable of less than 50mhz fsb.

Some early socket 5 boards can do 40MHz bus in order to accommodate 6x86-PR90.

The lowest my board can go is 50Mhz: http://www.uktsupport.co.uk/acer/mb/acv55-2.htm

GPA wrote:

You can always underclock your P166MMX to 75 MHz.

Yes, but with a P166MMX (P55C) you cannot get the same speed like a real P75 (P54C) which performs between P60 to P66.
A P55C @75MHz with the double cache of 16kb performs maybe >= P66.

But how are you going to get that kind of clock when the 1.5 multiplier is remapped to 3.5? Is there a trick I'm missing with my P55C/TX97?

gdjacobs wrote:

But how are you going to get that kind of clock when the 1.5 multiplier is remapped to 3.5? Is there a trick I'm missing with my P55C/TX97?

Exactly. The slowest this P166MMX can probably do is 2x50Mhz. Which is still respectably slow and not that far from replacing it physically with a P75 if push came to shove..

I would benchmark both P75 and P166MMX with caches disabled and enter into my database. 😀 Then you could see what performance levels each hit and make a decision based on that. Pick the one that gives you the most flexibility between your 233MMX and 486.