How do you overclock the P4?

I will cut-paste portions from an Email that I sent to Tom & co. earlier tonight and also add/modify for simplicity.

FYI the ability to lock the PCI & AGP frequencies are totally dependent upon your motherboard. For example the Asus P4B266 board allows you to run the FSB at 133(really 533 due to the 4X) and the AGP/PCI at exactly the correct 66/33 frequencies.

Here we go:

I have read your latest Intel P4-2200 vs AMD article and find your comments on overclocking to be wrong. You state that it doesn't make sense to overclock Intel boards because that generally also overclocks the AGP and PCI slots. The statements above are true for the 850 chipset, I do not know about VIA or SiS for sure but maybe. The interesting thing is that it doesn't have to be true at all for the 845 chipset, if the 33/66MHz PCI domain clocks stay constant while overclocking the FSB & memory the 845 will perform without fail everytime. In other words motherboards with the option to keep the PCI subsystem (AGP uses the same clocks) at a constant frequency while overclocking the processor and memory will give great performance increases. If you look at the "Intel® Pentium® 4 Processor in 478-pin Package and Intel® 845 Chipset Platform for DDR Platform Design Guide" located on the Intel web site (under developer) specifically page 187 you can see that there is a "Host_clk" spec'd at 100MHz and then other 66MHz and 33MHz clocks, the "Host_clk" and the "clk66" are both input's to the 845 MCH. Evidently by having seperate input clocks they have removed any requirement for FSB and AGP clocks to change together.

Additionally it is possible to play games whereby you push both the processor and the memory just to the point of failure thereby gaining maximum overclock performance. This is possible by selecting a lower multiplier on the processor, remember Intel doesn't seem to care if you want to run their chip slower just don't try to select a faster multipler. So let's look at an example (I modified this example for use as the Asus identified above):

Assumption #1 - use a socket 478 845 DDR system (Asus P4266)

Assumption #2 - use the 133 CPU, 66 AGP, 33 PCI jumper option

Assumption #3 - start with a 2.2G P4 system and DDR266 system

Assumption #4 - always populate the memory with the fewest DIMMs possible and always use single sided DIMMs of high quality (no not crappy Kingston, use some quality Micron or similar)-item #4 is of utmost imprtance and you don't often address this for your overclockers

Given these assumptions you will probably need to drop the CPU mulitplier otherwise the CPU will run at 2.9GHz (133MHz X 22 = 2.9GHz), probably between 18 and 20 would work which still gives you a nice performance jump from where you started because at a multiplier of 20 for example you are running the processor at 2.66GHz AND the FSB at 133 instead of 100 (really 533MHz due to 4X) AND your DDR memory at 353MHz instead of 266.

If you have a slower CPU then do the math for your system and set accordingly. You shouldn't expect more than 200 to 500MHz above the marked frequency before you start getting errors.

I have personally run these systems much faster than the above example on the CPU but the DDR memory stops around 350 or so. If your board has the option to bump the voltages go for it, CPU, chipset, and memory but don't get carried away 10%-15% is plenty. Also make sure you have good ventilation.

Adios,
chipsetfreak

Sorry to butt in, but do you know what the speed of the factory P4 fan supposed to be? My 1.5G fan won't turn over 3200 RPM and it's running around 43*C without overclocking. Is that normal? My older Celeron factory fan runs at 5400 RPM (although it is smaller)!

The Abit TH7-II is the only board with which you can push up the FSB without overclocking the PCI/AGP bus.

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I do not know what the factory fan is supposed to run at but 43C sounds reasonable. Per the 2.2G P4 datasheet which I found on the Intel web site the maximum case temperature is 69C for guaranteed operation, quite a bit more than 43C.

There are motherboards in addition to the Abit TH7-II that you can push the FSB without overclocking the PCI/AGP.

The Abit BL7 does, and I would bet that the new Abit BD7 series will though their manual is not posted yet ,the Asus P4B266 clearly identifies the option in their user manual as well as advertise it on their web page. With a simple 4:1 FSB CI ratio you can select FSB 133 and get PCI 33. Why do you say that the TH7-II is the only board which will do this?

False, if you overclock a PIII from 100MHz FSB to 133MHz FSB, the PCI divider drops and you end up with the PCI back at stock settings, even with the BX. For chipsets designed to go to 133MHz FSB, the AGP divider also drops and gives you stock speed.

Same with the P4 on overclocking motherboards. I heard that some chipsets for the P4 have an independant clock for PCI/AGP, but am not sure.

What's the frequency, Kenneth?