Overclocking: If You Do It, Do It Right!
It doesn't take much effort to increase the FSB speed by a couple MHz, but real overclocking (10% or faster clock speed) requires that you be much more thorough.
The CPU clock consists of the system clock, the Front Side Bus (FSB), and the multiplier. Pentium 4 systems work at 100 MHz FSB (quad-pumped, resulting in a performance that corresponds to a 400 MHz bus) and with multipliers between 14 (1.4 GHz) and 22 (2.2 GHz). Unfortunately, the multipliers on the Pentium 4 CPUs have been locked for years, so they cannot be altered. The only way to increase the CPU clock is to increase one of the multiplication factors - in this case, only the FSB is left.
It doesn't matter how the clock is increased: higher clock speeds usually require a higher CPU core voltage in order to run stably. Many motherboards in this review support core voltages of up to 1.85 V. That is enough to run a modern Northwood CPU at 2.5 GHz or even more, depending on the quality of your CPU cooling method.
As soon as the FSB clock is increased, both the AGP and the PCI clock will be increased analog to the FSB. Be careful: although it's unlikely that a component could be damaged, there are certain limits for PCI- and AGP cards. Usually you should stay below 40 MHz for PCI cards and below 85 MHz for AGP hardware.
Some of the recent motherboards give you the option of defining the PCI and AGP speeds relative to the FSB. Abit's BD7-RAID was one of the first motherboards to allow the FSB to be raised to 133 MHz, while the PCI and AGP interfaces can be clocked to specifications of 33 and 66 MHz, respectively. Even the memory stays at safe 133 MHz.
Further options for overclocking consist of increasing the AGP and the memory voltages (some motherboards can go up to 2.8 V instead of 2.5 V).
Reasonable Clock Speeds
The following table consists of our recommendations on how to run overclocked Pentium 4 CPUs. These statements are meant to be guidelines only and do not claim to be absolute, so it's likely that you can achieve higher clock speeds, though sometimes maybe ony lower. Everything depends on the quality of the individual processor. The only thing that you should always take care of is not to exceed ~40 MHz PCI and ~85 MHz AGP.
| Processor | FSB | PCI Clock | CPU Clock |
|---|---|---|---|
| P4 - 1700 MHz | 115 MHz | 38.3 MHz | 1955 MHz |
| P4 - 1800 MHz | 112 MHz | 37.3 MHz | 2016 MHz |
| P4 - 1900 MHz | 110 MHz | 36.6 MHz | 2090 MHz |
| P4 - 2000 MHz | 107 MHz | 35.6 MHz | 2140 MHz |
| P4 - 2200 MHz | 115 MHz | 38.3 MHz | 2530 MHz |
