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http://www.viahardware.com/faq/kt7/kt7faq.htm :
Why is my idle temperature so much higher under BIOS version 3R or later?
With previous BIOS versions ABIT set a bit in the BIOS CMOS (offset 52 bit 7) to "1" to enable the ACPI "HALT" function and cool down the CPU temp in idle mode. This, whilst allowing cooler CPU operation, is against the advice of AMD and VIA. Under earlier AMD processors, however, this modification allowed the system to idle cooler and had no ill effects. However, it was been found with newer 133MHz FSB processors running at 1333MHz and higher, that this software cooling can cause severe stability problems - especially under Windows 2000. As a consequence, in all ABIT BIOS releases after version 3R, ABIT have set this bit to "0" - the value recommended by AMD and VIA. This allows the motherboard to be stable with all AMD processors at the expense of an increase of 5-10 degrees Centigrade during idle (from approximately 35 degs C to 45 degs C). This will not harm your motherboard or processor. Note that this CMOS setting is widely used by other KT133/KT133A based motherboards. Note that if your processor is slower than 1333MHz then you can revert to the previous setting of the BIOS by using H-Oda's WCPREDIT and WCPRSET programs to modify this register value. If you are using Hex mode in these programs then change register 52 from 6B to EB to re-enable the software cooling (on some KT133A-based machines you may need to change form 6C to EC). See downloads page for programs. This functionality is also included in the CPUcool and VCool tools.