Underclocking? Can I use a faster cpu at a lower speed?

[monty365]

I have a Supermicro P6DBS dual Pentium II/III motherboard. I have been running 2 333mhz PIIs at 400mhz sucessfully for a long time.

Now I want a little more speed. My board is supposed to run up to 600mhz PIII at 100mhz bus. My question is can I run faster cpus, like 650/133 at the 600/100 that is supposed to be the top end for this board. Has anyone done this succesfully? With dual cpus?

My reason being that the faster cpus are curently cheaper than the recommended 600/100. Any information will be appreciated

 

[John]

Well the 650 @ 133 is actually a P3 667. It has a clock of 5 and a FSB of 133. The clocks are locked, so you would run into a problem. What clock multiplier does your bios or jumper go to?

 

[Generalen]

Well here is a problem, the 5X133=667 as john said and your motherboard only support 100mhz bus then u only will get out (5X100=500) 500mhz of the cpu kind a waste of money I think if u not plan to upgrade whit a new motherboard in the nearest future u should go whit the 6X100=600 processors I think.

 

[monty365]

Hey John,
My jumpers allow me to set the multiplier from 3 to 7.5 with the bus at either 66 or 100, no 133 available.

 

[RickH]

You can't set the multiplier on a PIII. R

 

[ledzepp98]

so get the 750 at 7.5x100, your mobo supports that. if it's a price thing then get a slower cpu but stick with the 100mhz fsb cpu's since, as people have mentioned, it will be very underclocked if you run a 133mhz fsb pcu on a 100mhz fsb due to the multiplier lock

 

[Kwad Guy]

If your board will only support up to 600Mhz/100Mhz FSB, then
it will not boot with ANY Coppermine, and all PIII 133Mhz FSB chips
are Coppermines. The reason is the on-board voltage regulator
in a board that doesn't support Coppermines can't provide the
required lower voltage...

You can get around this issue using a slotket that allows
voltage adjustment, although you will have to run with voltage
set to 1.8V, usually 0.10-0.15 V higher than spec.

Kwad

 

[John]

Kwad Guy brings up a very valid issue. Your clock mult will support a 750MHz cpu, but may not support a coppermine. I would give their tech support a quick call to verify our thoughts.