The CPU (Central Processing Unit) is the main microprocessor and the heart of any computer device. There are two main types of CPUs for personal computers: The x86 processors (IBM/Intel originally, CISC based protocol) and the RISC based processors. Current mainstream CPU designs for desktop computers now are CISC processors that incorporate some RISC technology. Most of them also feature multiple processing cores on a single CPU, simply called cores. RISC processors have been used in personal computers, but are now mainly used in enterprise computing (servers, data centers) and in certain game consoles.
Main manufacturers of CPUs for personal computers are Intel, AMD and VIA. Brand names of Intel include Celeron, Pentium, Xeon and Core. Brand names of AMD include Phenom, Duron, Athlon, Sempron, Turion. Brand names of VIA include Nano, C7 and Eden.
CPU models require specific sockets in which they can be mounted, e.g. Socket AM2, Socket 775, Socket A, LGA1366, etc.. Therefore, a CPU will only fit in specific motherboards, because the sockets are permanently soldered onto the motherboard.
CPU performance is roughly determined by clock speed (the speed at which a microprocessor executes instructions), the number of cores and its memory-architecture. In theory the higher the number of cores, the higher the amount of instructions that can be simultaneously processed. The processing speed is then determined by the clock speed of each core and how fast data can be transfered to and from memory.
Through smart power management (ACPI), task-specific decrease of clockspeed and aggressive shut down of unused sections or even complete cores (e.g. Intel's SpeedStep, AMD's Cool'n'Quiet and PowerNow!), the average power consumption of the CPU will be far lower (30-50%) .
CPUs are tradable goods in their own right, mostly as an upgrade product for the consumer market (if it fits the socket) and are performance-tested by various magazines for the consumer-market.
For more background on CPUs for personal computers and datasheets specifying TDP and energy use in various standby modes see intel.com, amd.com and via.com.tw.
Courtesy of the French Energy Agency ADEME, Future Electronics project. Expanded by VHK.