Depending on the motherboard features and chipset, both the AGP and PCI bus speeds may also be a problem. Chipsets such as the nForce and K266A fully support only the 100 and 133 MHz FSB, while the new KT333 includes both of these, and some manufacturers have even activated the 166 MHz FSB. In the case of many VIA boards, at least the correct PCI divider for the 166 MHz FSB is present and accounted for, but the exact level of support for a 166 MHz FSB depends on the board itself. What this really means is that some motherboards may allow 100, 133 and even 166 MHz FSB speeds, while maintaining standard 66 MHz AGP and/or 33 MHz PCI settings. As the saying goes, use them if you have them.
If you run at a FSB higher than the standard settings, you can often find that you are inadvertently overclocking the AGP and PCI bus as well. With newer video cards, ramping up AGP speeds isn't that big a deal, but for optimum stability you'll want to stay as close to the 33 MHz specification of the PCI bus as possible. Most PCI cards should be able to run up to 35-36 MHz without hitch, but some lower quality PCI cards can experience problems at frequencies above 33 MHz. IDE hard drives may also be unwilling to run on a high PCI speed, with data loss or system crashes being the result.
CPU Core Voltage
Increases to the CPU core voltage will most likely be needed, and here you should also tread with care. Increase core voltage only when needed and use the smallest increment offered by your particular motherboard. Remember that each increase in core voltage carries with it a commensurate rise in core temperature. The hardened overclocker will already have a CPU cooler that far exceeds their current CPU specs, with headroom for future overclocking built right in. Even then, keep a close eye on overall CPU and case temperatures and look to maintain a balance between CPU speed, core heat and overall system stability.
There are few hard and fast rules regarding overclocking using the FSB, as so much depends on the motherboard features and the peripherals used. Basically, it involves a slow and steady progression up the FSB ladder, keeping track of AGP and PCI speeds, as well as continually testing overall stability. Never just rack the FSB to some outlandish number, as this is a very risky maneuver and hardly ever works. We've seen some hard drives that conk out at high PCI speeds, as well as the odd NIC or SCSI adapter that simply will not work, or may even be physically damaged, if the PCI bus is pushed too far.
