Overclocking and underclocking ?
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.
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Pushing the limit of wait state in bios and what happened ?
In every computer, there is the bios, which runs the computer virtually. It is an operating system, though very crude, runs it with an iron hand. You can not change anything except by flashing it again with updates or upgrades. Bios tempering is never recommended, because of the risk of flashing errors; and bios are limited by the size of eeprom or flash device in mb(currently 10). Some bios are still 1-4 mb, if you try to cram more features into the small flash; you have to give up some features.
So, once I determined that Intel440BX has 6.5x multiplier limit and FSB is 100mhz; the maximum cpu frequncy is 650 mhz. I bought a P3 866mhz cpu for it. I put it in and it started to run flawlessly at 100mhz FSB instead of 133mhz.
There is, however, an error in reading SMBus info. The cpu is listed as Pentium Pro 500mhz. Serial Presence Detection got no data. This could be due to the Phoenix bios complexity. Award bios probably will read correctly.
This computer now runs 1800+ MIPS according to Sis Sandra, equivalent to P3 750 mhz performance.
If the wait state can be changed in shadowed bios in drams on the fly; thus computers can be run at 866 mhz or even overclocked 10%(on other motherboards with PLL chip; this motherboard will run higher fixed multiplier if wait state can be accomodating). So, there is hope that you can always use Linux or Microsoft operating system to change bios at will without any memory boundaries to worry about. Someone reading this might just write a program to change bios in the drams by reading all the data from the cpu correctly in the control center? Underclocking can definitely be benefited then.
This, of course, means you can override speed steps and multipliers, and all kinds of wonderful changes in the way cpu will be run at any time.
Celeron vs. P3 and winning as a strategy ?
Many 370 socket motherboards can be interesting with the used cpu prices near bottom on ebay.
Its time to re-examine your upgrading strategy?
First choice is Celeron to replace P3? Am I foolish of what?
New Celeron have steppings of 8/6(1) which is very fast. Faster than P3 of older steppings such as 8/3(2)?
When I put in 700 mhz Celeron, its slow with old steppings. when I put in 633 Celeron and run it overclocked at 75 mhz FSB, it became very snappy with Via 4in1 chipset AGP softvideo of S3 Pro Salvage+.
Sis Sandra gives it 731 mhz, and PR854 rating. It settled down at 2024 mips speed and is equivalent to a P3 750 mhz 133 mhz FSB rating at 2025 Mips. Not bad for a 633 Celeron.
Footnote:
Celeron is 633/128/1.65v. the motherboard(Alton V(ia)605A) has 1.78 core voltage supply only, which is ideal for overclocking, a little overvoltage to get the transistors to run slightly hotter and faster. The heatsink is one size larger than Intel official heatsink and fan combo, originally made for IBM(a Taiwan cooler).
The operating temperature without overclocking was 33 degrees C(case temperature was 32 degress C., when it runs overclocked it is 35.7-36.2 degrees C depending on how intensive the cpu was run(case temperature was 33 degress C)..
Footnote:
One of the later batch of PPGA 400 mhz celeron has steppings of 6/5(0), which even though Mips is 1346 is very fast because of wait state of less than 3 turns. there are lot numbers on each cpu. These lot number can be matched for dual cpu motherboard, such as P3 SL45Z. Then there are cpu serial number on each cpu.