Since multiplier manipulation on Pentium 4 CPUs is unattainable, because the CPUs are locked and there is virtually no way to unlock them, the only way to increase a Pentium 4 CPU speed is by manipulation of the FSB. Since the FSB will be increased a lot, my recommendation is to overclock only if you have a motherboard that can handle overclocking and that has an AGP/PCI bus is locked on a fixed frequency. If the AGP/PCI bus cannot be locked, that means that the AGP/PCI devices will get their bus overclocked as well. That gives nearly no increase in performance, however on the other hand video cards and hard disks among other components do not like that at all. The hard disks might get corrupted or permanently damaged, the video cards unstable, producing corrupted images or not work at all. That is why overclocking with a motherboard that doesn’t feature these locks is not recommended at all, the risk for the other components is too high, and so if you proceed make sure you can take the risk. The recommended motherboards for overclocking are the ones which carry the Intel 845 or Intel E7205 (Granite bay) chipset for the CPUs that have an FSB of 533 or less and those that carry the Intel 865 (Springdale) or Intel 875 (Canterwood) chipset for CPUs that have an FSB of 800. Also, for overclocking the lower model CPUs are usually best. The higher end CPUs are already near the end of their abilities and will hit a wall fast, keeping the FSB down, plus the lower models can overclock just as far and good since the cores are virtually the same.
Memory overclocking and performance:
On Pentium 4 platforms, memory is the thing that speeds up the whole system and the key for performance. The memory cannot run any faster than the CPU FSB speed, even set higher it will just follow the CPU FSB clock and lower the performance to that level. Since the processors are Quad-Pumped their bus speed is 4 times the FSB, not 2 like on Athlon systems. So the memory is nearly impossible to be bottlenecked by the CPU. However each motherboard and processor combination has its own memory requirements. One thing that you should not worry too much about are the timings, these matter little on Pentium 4 systems since the memory bandwidth can all be used up. Of course if you can set them low they will help, but very little. Raw MHz speed is what matters most.
On Intel 845 chipset motherboard you will need the fastest memory that you can get. When overclocking the processor on such a motherboard the memory will climb a lot since it’s already running ahead of the processor. Especially if you have a lower end model processor, the FSB might fly way too high. There are divider settings which you can manipulate to keep the memory speed lower, however that will lower the performance of course.
On an Intel Granite Bay chipset motherboard, you won’t require too fast memory but 2 modules of it since the motherboard supports Dual Channel DDR. That means it will nearly double the memory speed of the modules set on it by splitting data to each module instead of sending the data all at one module. Since this motherboard supports only 533FSB CPUs and Pc2100 (DDR266) memory and the memory speed is doubled, the memory will run at 266×2=533MHz. Bingo, the maximum possible speed that the memory can have without having a bottleneck. When you raise the FSB, both the processor and memory speeds will be raised but will always stay 1:1. The FSB can’t go too high so 2 good modules of Pc2700 memory should be sufficient for overclocking.
On Intel 865/875 chipset motherboards you will certainly need the fastest memory possible that you can get, certainly faster than Pc3200 memory and 2 modules of it as well. Since those motherboards support the 800FSB processors, the Pc3200 memory is the minimum requirement and 2 modules of it as well since the motherboards support Dual Channel DDR. Of course if you overclock there are dividers to lower the memory speed and you certainly will use them if you have a lower model CPU which will make the FSB fly, but it will be more than nice if you can keep the memory speed over 220MHz (440DDR). This way the memory bandwidth will be extremely large and that translates to excellent performance.
Voltage settings and cooling:
To overclock any component, after a certain limit you may have to increase the voltage supplied to it. For Pentium 4 CPUs that is dangerous enough because the CPUs suffer a lot from EMI. Any voltage over 1.75v will kill the CPU sooner or later, no matter the cooling. However if set at or under 1.7v it will be ok for over a year, provided that the cooling is sufficient. Most Pentium 4 CPUs will overclock well enough with 1.6v or less, so usually there is no need to raise the voltage that much. Always keep the temperature of a Pentium 4 CPU under 60c –under load-. Since Pentium 4 CPUs feature a heatspreader and they will radiate medium to high amounts of heat continuously, unlike Athlon CPUs which radiate extreme amounts of heat for short periods and over a small core, the Pentium 4 CPUs favor heatsinks that are large and have a copper base with aluminum pins/fins, like the Swiftech MCX478, or copper heatsinks of very large size and medium-high flow fans, like the SLK-900 paired with a proper fan.
For memory voltage, anything up to 2.7v is covered by any company warranty. Some companies cover more, like Geil which for some modules they give warranties up to the very high 3.1v. I’d suggest setting the memory voltage to 2.8v unless you use generic memory. This kind of voltage will lessen the life of the module to about 3-5 years if it’s of decent build quality. I don’t think any user would keep a system that long, especially overclockers which will buy new ram within 6-12 months (I told you that it is addictive). By using that voltage setting, you can limit your modules abilities and still be on the safe side. Of course if any company warranties above 2.8v for the modules that you have, like some OCZ or Geil modules, use up to that limit if you motherboard will allow you to do that. But if you have generic memory, skip that and leave voltage at the stock 2.5v.
About the chipset cooling, most motherboards have a passive heatsink. In order to reach high FSB speeds you better improve that. If the heatsink is of decent size (side longer than 40mm) you can simply get a small fan that will fit the heatsink and screw it or glue it on. It is very easy to pick one, just measure the side of the heatsink and get the according fan. For a heatsink with 50mm side you will need a 50mm fan, for example. If it is passive and very small, you better get a decent chipset cooler like the ThermalTake Tiger.
Basic procedure and testing loop:
That is something quite easy on Pentium 4 systems. Just set the memory timings to SPD, the voltages where you feel they are safe and you are good to go.
Proceed by raising the FSB in 5MHz increments, testing stability each time. To test the stability, run Prime95 and/or SuperPi for 15-20 minutes. If they give no errors, go further. If they do, check the memory frequency. If it went too high, use a divider (like 1:1 for an 845 or 5:4 / 3:2 for an 865/875 chipset) and try again to see if it is stable. If it is, leave the divider and go further but if it isn’t just reset the divider to its previous value, which is your maximum system speed attainable. Also if you won’t go enough further (at least 10MHz more) even with the use of the divider, remove it and clock the system down to the stable setting with the higher divider, it will probably be better. To test the stability totally, let it run a Prime95 test or loops of 3dmark 2001 for hours. If it isn’t stable, back it down a couple more MHz. Keep an eye on the temperatures also since that’s when your system will work at the maximum potential and heat up the most.