Everyone wants overclocking, it can speed up your computer without extra cost. Semiconductor manufacturers often mislabel their products and you could be lucky. I buy a number of cpus just to get some that can overclock 33%. It became a macho thing for enthusiasts to brag about their overclocking(bigger does matter).

Nobody ever brags about underclocking. Buying faster cpus just to run them slower? Is speed steps the most famous underclocking events? No. I buy P3(256/13) to use in place of P2 or celeron(128/100) 100 mhz cpus.

Well, first you have to examine the motherboard to find the sc1182 VRM voltage chip which will extend down to 1.78 volts for cpu core voltage(1.5-1.75v). Then you can use fcPga package. You might have a slot1 motherboard which can use fcPga socket conversion.

Once you decided underclocking to reduce heat for server application; you buy used p3 with front side bus at 133 mhz but run it at 100 mhz(a 33% speed reduction, but the L2 cache size improve 20% in speed over celeron). It runs luke warm, when you touch the official Intel fan and heatsink fins. I am using this computer with 733 P3 running at 550 mhz now posting here, but waiting for my 866mhz P3 won on ebay to run at 650 mhz. The computer with old ESS ISA dialup modem(54,666) is very snappy on Intel SE440BX motherboard. Bios is old and can only handle multiplier of 6.5x. Which means wait state limits the cpu to 650 mhz max. Wait state is only 3 turns, meaning you waste 3 clock cycles everytime you send atm(asychronous transfer mode) codes, compared with newer cpus with 20 clocks delay typically.

Have fun with your older equipment in the dark continent? There are still speed you can get from wait state advantage with underclocking and larger L2 cache free of charge that comes with these older cpu people throw away.