Pentium 1 underclocking

[jedandjess]

Hi all. I wonder if anyone out there can help me with this different kind of problem, maybe the older ones will. I have a pentium 1 system which i recently built, with a P1-120Mhz processor installed (socket 7). I have set the multiplier to it's lowest setting, and the chip is running at 75Mhz . The problem is, for the task I want the machine to perform, this is still too fast. I am looking for around half the speed of a P75.
Has anyone got any advice how I could lower the overall performance? Would changing the voltage work and if so do I increase or decrease the voltage? I'd prefer to slow the CPU down with hardware changes rather than a program like moslow as it's more reliable.

Any help appreciated I've asked in other forums but no one seems to know, I just get refrered to Moslo

cheers

Jedandjess

 

[z-lite]

I have set the multiplier to it's lowest setting, and the chip is running at 75Mhz...I'd prefer to slow the CPU down with hardware changes rather than a program like moslow as it's more reliable.

As I understand it, O/U clocking a CPU deals with the FSB and multiplier. If the motherboard or BIOS doesn't give you the option or you can't adjust it any more, it's time to move onto a software solution. But why run a slow CPU at an even slower speed? What purpose do you have with it?

 

[compslckr]

sounds like a strange problem... "i can't get my cpu to run slow enough"

anyways check the motherboard for jumpers that might control the fsb, but i dont think you are going to get many options with stuff that old

 

[quadnad]

yeah, you'll be looking for dropping the fsb and multiplier in your bios (or as compslckr said jumpers on the mobo, but you might not have those things available on an older board). you'll then be able to drop the voltage once you've underclocked it sufficiently.

keep in mind that dropping the voltage won't cause the cpu to run slower, it will just make it less stable if its clocks are too high.

To be honest, if you want a proc that runs about half as slow as a seventy five mhz pentium, buy/build a 486.

 

[spotdog14]

yeah, you'll be looking for dropping the fsb and multiplier in your bios (or as compslckr said jumpers on the mobo, but you might not have those things available on an older board). you'll then be able to drop the voltage once you've underclocked it sufficiently.

keep in mind that dropping the voltage won't cause the cpu to run slower, it will just make it less stable if its clocks are too high.

To be honest, if you want a proc that runs about half as slow as a seventy five mhz pentium, buy/build a 486.

i just threw away my old 386 machine because win 3.11 wouldnt boot anymore...

 

[Burticus]

A free method to cripple the hell out of your chip is to DISABLE L1 and L2 cache (either by bios, jumper on the mlb, or by pulling the dram cache chips off the mlb!). That'll kick your cpu output in the jimmy by as much as half!

75 (50 x 1.5) is the lowest stock setting of a socket 5/7 pentium. Doubtful the mlb would even have a 1x multiplier jumper, but anything is possible.

Also, if your board is extra special "old school" and has a fixed crystal for clock gen then you should be able to throw a lower speed cystal in. Keep in mind the crystal freq is double the fsb.... so 50 mhz would say 100 on the crystal. Crystals are 5-10 bucks tops. Downside is you might have to heat the solder to get the bastard out....

If none of that makes sense, look for one of these bad boys on your motherboard. If it says 100mhz on the top, that's your guy. I doubt anything slower than a 66mhz would work, but what the hell.

http://www.vectron.com/products/ocxo/ocxo_index.htm

Although now that I think about it I haven't seen a crystal on anything faster than a 486, so you're prolly out of luck with my ramblings.