The current CMOS technology in which modern processors are manufactured not only consist of transistors but also capacitors and resistors. Resistors create heat that must be conducted away from the processor. This tend to be easier with higher temperature gradients. This is the reason that processors are not only equipped with large heat sinks but also actively cooled with fans or Peltier cooling elements. Higher temperatures accelerate effects like electromigration (see the OverClocking Guide ) or oxide breakdown that might eventually lead to failure. A temperature increase of 10 degrees can significantly reduce the normal lifespan of a processor. This not only holds for the processor but also for the VRM (voltage regulation module) that supplies the I/O and core voltages. This is most prevalent in older or poor quality mainboard designs that employ passive VRMs. These generate additional heat in the PC.
How These Utilities Work
All of these small utility programs run HLT commands to idle parts
of the CPU, so that they don't generate heat while they're idle. HLT commands put the processor into suspend mode. Under normal circumstances the CPU isn't always active but spends much time waiting for the keyboard, harddisk or CD-ROM. What could be more logical than to turn off the CPU for that period? That's exactly what the HLT machine instruction (Opcode F4) does. Whenever the CPU encounters a HLT instruction the clock is halted and the CPU enters suspend mode until an interrupt, NMI or reset occurs. With the creation of power saving processors from companies like Cyrix, Intel and AMD, the HLT instruction acquired an additional property. When "Suspend on HLT" is enabled in the configuration register the processor not only stops on HLT but also enters this power saving suspend mode.