Not all systems are the same- nor are all CPU's. The basic raise the clock, increase X speed generally works, but there are usually some catches.
Athlon XP's
You may have multiplier control, and you have FSB control. A PCI lock is necessary to keep the AGP/PCI bus in spec, or your overall FSB will be limited greatly. With an Athlon XP, CPU speed is determined by FSB*CPU multiplier, and ram speed is determined using a divider of the FSB. It’s highly recommended to keep the ram 1:1 on Athlon XP systems, for stability, and performance reasons. An alternative to Bios overclocking, is clockgen- but with the Athlon XP platform, it is very sensitive to on the fly clock changes, so it will often crash the system. Clockgen is generally not recommended for this type of system.
Athlon XPs love voltage in general. The maximum "safe" voltage for most people running 24/7 should be around 1.9v. Extreme cooling allows the use of 2.1-2.3vcore, but only if you don't care especially for the life of it!
Pentium 4's
Pentium 4's are all about one thing. Clockspeed. They were designed to scale well, and did pretty well until the prescott core hit. While overclocking pentium 4's there has been the Sudden Northwood Death Syndrome, or better known as SNDS, which was too much voltage, or the cpu's just dieing, but that has pretty blown over, with the disappearence of the northwood core. Prescotts are now the main P4, whilst running hot, can scale to amazing speeds under the right settings. You normally have fsb, the pci lock, and sometimes a 14x multiplier to mess with. Multipliers are locked on P4's, however some people prefer to spend the extra cash to hunt down engineering samples to have multiplier control. As usual, clockgen works best with newer chipsets.
Athlon 64's
The Athlon 64 is possibly one of the most confusing of the processors, but offers some of the most overclocking flexibility available today. Since AMD moved the memory controller onto the CPU, it really messed with the way you overclock these systems. In some ways, it’s a wonderful thing, but it has its downfalls.
The CPU speed is determined by the HTT*CPU multiplier. The CPU uses the Hypertransport link to communicate with most of the motherboard, and overclocking this has no tangible performance difference, and like the PCI bus, running it too far out of spec will cause stability problems. To fix this, you change the LDT multiplier, to keep it within 800mhz for socket 754 Athlon 64's and 1ghz for socket 939.
With the memory controller on die of the Athlon 64, it is now capable of running much greater speeds than the traditional Northbridge FSB. It is now set to run 1:1 with the CPU speed. In turn, overclocking the CPU results in overclocking the memory controller as well. This has an added bonus- Higher CPU speed returns lower memory controller latency! However, this also screws up the .5 multipliers, and will return a slightly different memory speed than expected. AMD does not support, nor recommend using .5 multipliers, and with such a wide range of HTT to choose from, it’s unnecessary to use anyways.
Memory speed is determined by dividing the CPU speed. There is no longer a "1:1" ratio, so dividers will have no impact on performance whatsoever. 10x300htt using 250mhz memory will perform exactly as 12x250 set to 1:1.
Alternatively to regular Bios overclocking, clockgen works fantastically on these platforms! You have a very effective HTT range to choose from, along with multiplier control from within windows. The multiplier control is excellent for turning your CPU down to 1ghz while surfing/checking e-mail, and cranking it back up to full speed when you get ready to start a game up.
Currently, VID (voltage) control does not work for most boards.
Some examples of an Athlon 64 Bios screen:
Thanks to angry_games over at
DFI-street for the use of his great bios screen examples!
Core 2 Duo's
Coming soon!