Use 2.7 and see if it is stable.

If it's not (which I doubt), just use 2.9, as it's still within safe limits.

I tested one of my 233MMX and it would run fine even at low 2.2V. So just use 2.7V or even lower if you won't overclock. It will run cooler.

Let it run for one hour at full load. Only then you know if it's stable. Voltage matters when the CPU is getting hot.

Which MMX CPU exactly? Some of the later PPGA (black&metal case) versions were hugely overengineered and could run at 300MHz at stock voltage (2.8V) or be underclocked to 2.2V (as kixs did) at stock speeds. The earlier CPGA versions could be pickier, but even there 2.7V should easily work.

To generate that one hour full load, use SuperPI, it's uniquely sensitive to errors from overclocking/undervolting. If SuperPI works, pretty much anything else will too.

P1 200MHz MMX= "SL27J".
Upgrade to ceramic P1 120Mhz. Took 2h to install Win98SE with it and I had industrial CF-card and all max.RAM in it for fast speed. So I bought a better CPU.

user33331 wrote:

P1 200MHz MMX= "SL27J".
Upgrade to ceramic P1 120Mhz. Took 2h to install Win98SE with it and I had industrial CF-card and all max.RAM in it for fast speed. So I bought a better CPU.

That's one of the good PPGA CPUs.

Intel spec:

VID Voltage Range 2.7V-2.9V

So 2.7V is actually within official spec. No reason whatsoever to go for 2.9V.

dionb wrote:

Some of the later PPGA (black&metal case) versions were hugely overengineered and could run at 300MHz at stock voltage (2.8V) or be underclocked to 2.2V (as kixs did) at stock speeds. The earlier CPGA versions could be pickier, but even there 2.7V should easily work.

From what I recall, the CPGA and PPGA versions of the PMMX were available at the same time, neither being older or newer than the other. It always confused me why intel offered the chip in two packages, and my only conclusion is they must have had a lot of leftover CPGA packages from the classic Pentium line they wanted to get rid of.