Hack #25. Control CPU Clock Speed from the BIOS
Increase your CPU speed with parameters controlled by your BIOS.
After you've determined your present CPU speed [Hack #6] and [Hack #24]
Some system boards give you everything you need to adjust clock speed from within the BIOS setup. Figure 3-21 shows very basic CPU speed control available in the Award BIOS of an ECS system board for an AMD Athlon CPU.
Figure 3-21. This Award BIOS setup program provides only CPU clock control with a default of 166 MHz
Starting with a system with an AMD Athlon XP that clocks at 1.9 GHz, with the original or default speed setting based on a 166 MHz CPU clock and an internal CPU clock multiplier value of 11.5 (166 11.5 = 1.91 GHz), adjust the base clock speed up incrementally until the system fails to boot up or function reliably. Changing the base CPU clock speed to 185 MHz with the same fixed multiplier value (11.5), the CPU makes it up to 2.13 GHz (11.4% faster), runs reliably with no hacking other than this speed setting, and delivers a measured 11.40% performance increase per Sandra benchmarks [Hack #23] .
Warning
Changing the CPU clock speed also affects the operating speed of other system components, most notably the Front Side Bus (FSB) that interfaces with the system's chipset and memory. If an overclock attempt fails, check the speed of your RAM and consider the limitations of the system board ...
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