Basics of CPU

Overclocking PII
Optimal speed
Setting CPU speed

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Basics of CPU Speed
Two variables determine the speed at which your CPU runs: the frontside bus speed and the clock multiplier. By manipulating these variables you determine the CPU's clock speed.

Understanding Bus Speed
The CPU uses the FSB (frontside bus, also called the system bus) to communicate with system memory and peripherals. (The backside bus, on the other hand, connects the Pentium II to the L2 cache inside the Pentium II cartridge.) Pentium IIs rated at 350 MHz and faster operate by default at a frontside bus speed of 100 MHz, while Pentium IIs rated at 333 MHz and slower run at 66 MHz.

Peripherals residing on the PCI bus, however, are designed to operate at 33 MHz. The clock divider sets the clock rate for the PCI bus as a fraction of the frontside bus speed. On motherboards with a frontside bus speed of 100 MHz, for instance, the clock divider is set to 1/3 that speed, to deliver a PCI bus clock speed of 33 MHz. On motherboards with a frontside bus speed of 66 MHz, the clock divider is set to 1/2 that speed.

FSB Speed x Clock Multiplier = CPU Speed
The motherboard chipset controls the clock multiplier, which, in conjunction with the FSB speed, determines the core speed of the CPU. Multiply the FSB speed by the clock multiplier to get the CPU speed. For instance, a 350-MHz Pentium II runs at a default FSB speed of 100 MHz with a clock multiplier of 3.5 (3.5 x 100 = 350).

By manipulating the clock multiplier and/or the FSB speed, you can increase the core speed at which the CPU runs. Here's a list of default settings for Pentium IIs.

Default Settings for Pentium IIs

CPU Speed FSB Speed Clock Multiplier
233 MHz 66 MHz 3.5x
266 MHz 66 MHz 4.0x
300 MHz 66 MHz 4.5x
333 MHz 66 MHz 5.0x
350 MHz 100 MHz 3.5x
400 MHz 100 MHz 4.0x
450 MHz 100 MHz 4.5x

Optimal speed for the CPU