Editing Front-side bus (section)

==Related component speeds==

[[File:Motherboard diagram.svg|thumb|300px|A typical chipset layout from the Pentium II/III era]]

===CPU===

The [[frequency]] at which a processor (CPU) operates is determined by applying a clock multiplier to the front-side bus (FSB) speed in some cases. For example, a processor running at 3200 [[Megahertz|MHz]] might be using a 400&nbsp;MHz FSB. This means there is an internal [[CPU multiplier|clock multiplier]] setting (also called bus/core ratio) of 8. That is, the CPU is set to run at 8 times the frequency of the front-side bus: 400&nbsp;MHz × 8 = 3200&nbsp;MHz. Different CPU speeds are achieved by varying either the FSB frequency or the CPU multiplier, this is referred to as [[overclocking]] or [[underclocking]].

===Memory===

{{see also | Memory divider}}

Setting an FSB speed is related directly to the speed grade of memory a system must use. The memory bus connects the northbridge and RAM, just as the front-side bus connects the CPU and northbridge. Often, these two buses must operate at the same frequency. Increasing the front-side bus to 450&nbsp;MHz in most cases also means running the memory at 450&nbsp;MHz.

In newer systems, it is possible to see memory ratios of "4:5" and the like. The memory will run 5/4 times as fast as the FSB in this situation, meaning a 400&nbsp;MHz bus can run with the memory at 500&nbsp;MHz. This is often referred to as an 'asynchronous' system. Due to differences in CPU and system architecture, overall system performance can vary in unexpected ways with different FSB-to-memory ratios.

In image, audio, video, gaming, [[Field-programmable gate array|FPGA]] synthesis and scientific applications that perform a small amount of work on each element of a large [[data set]], FSB speed becomes a major performance issue. A slow FSB will cause the CPU to spend significant amounts of time waiting for data to arrive from [[random-access memory|system memory]]. However, if the computations involving each element are more complex, the processor will spend longer performing these; therefore, the FSB will be able to keep pace because the rate at which the memory is accessed is reduced.

===Peripheral buses===

Similar to the memory bus, the PCI and AGP buses can also be run asynchronously from the front-side bus. In older systems, these buses are operated at a set fraction of the front-side bus frequency. This fraction was set by the [[BIOS]]. In newer systems, the PCI, AGP, and [[PCI Express]] peripheral buses often receive their own [[clock signal]]s, which eliminates their dependence on the front-side bus for timing.

===Overclocking===

{{main | Overclocking}}

[[Overclocking]] is the practice of making computer components operate beyond their stock performance levels by manipulating the frequencies at which the component is set to run, and, when necessary, modifying the voltage sent to the component to allow it to operate at these higher frequencies with more stability.

Many motherboards allow the user to manually set the clock multiplier and FSB settings by changing [[jumper (computing)|jumper]]s or BIOS settings. Almost all CPU manufacturers now "lock" a preset multiplier setting into the chip. It is possible to unlock some locked CPUs; for instance, some AMD [[Athlon]] processors can be unlocked by connecting [[electrical contact]]s across points on the CPU's surface.  Some other processors from AMD and Intel are unlocked from the factory and labeled as an "enthusiast-grade" processors by end users and retailers because of this feature.  For all processors, increasing the FSB speed can be done to boost processing speed by reducing [[latency (engineering)|latency]] between CPU and the northbridge.

This practice pushes components beyond their specifications and may cause erratic behavior, overheating or premature failure. Even if the computer appears to run normally, problems may appear under a heavy load. Most [[Personal computer|PC]]s purchased from retailers or manufacturers, such as [[Hewlett-Packard]] or [[Dell]], do not allow the user to change the multiplier or FSB settings due to the probability of erratic behavior or failure.  Motherboards purchased separately to build a custom machine are more likely to allow the user to edit the multiplier and FSB settings in the PC's BIOS.