The Power Calculator Help page documents methods, terminology and references used in the online power calculator. The computer hardware included for calculation: Motherboard, CPU, Graphics Card, Hard Drive, Other Drives, Memory, PCI Expansion Cards, External USB, and Case Cooling Fans.

General System Description. Classification used to size motherboard sans CPU, expansion cards, and memory. Typically between 20-50W.

CPU. Besides high performance graphics cards, the CPU will consume more power than any other hardware component. For this reason, our calculator has focused on providing extensive CPU coverage (over 1000 models) and information for Intel and AMD processors. Besides Thermal Design Power (TDP) or equivalent value, each selected CPU will also provide on board cache, core design, codename, socket, and available part numbers. This information has been compiled from the AMD, Intel, Wikipedia, and CPU World.

Graphics Card. Unlike CPU manufacturers, many video card makers do not publish power requirements. This is unfortunate on a number of levels, the primary being adequate information for proper power supply selection. X bit labs has conducted several outstanding studies on graphic card power consumption. The most recent study was performed across different manufacturers and categories. Our calculator takes an average from each of the 5 categories. The categories are presented as selection options.

Hard Drive. X bit labs and tom's hardware both have performed detailed hard drive power consumption tests. The power calculator has synthesized results from both studies. For most application users, the best approach is to select based on hard drive size (3.5", 2.5", or 1.8") with 3.5" being the most common desktop form factor. Also included from the X bit report is 35 common hard drives by manufacturer and model. Drives consume the most power upon start up. Both reading and writing are also power intensive operations, nearly matching startup in certain cases.

Other Drives. Other drives such as CD-ROM, DVD-ROM, CD-RW, DVD/CDRW Combo, and DVD-RW/DVD+RW consume maximum power values between 20-30W.

Memory. Memory is one of the more difficult hardware components to accurately measure. A memory module is composed of several chips or integrated circuits. These circuits require power to operate and define "how much". The Calculator makes an educated guess based on the memory technology and number of modules.

PCI Expansion Cards. The PCI specification requires expansion cards to communicate power needs. Two pins (PRSNT1# and PRSNT2#) are used to signal maximum power of 25W, 15W, or 7.5W. For simplicity the calculator take an average of these values and assigns each PCI Expansion card 15.8W.

USB Devices. External USB devices are consume very little power. The calculator assigns 0.5W for each device. A detailed analysis of several USB components can be found on tom's hardware.

Case Cooling Fans. Case cooling fans will draw between 0.2 - 2.0W depending on fan speed. A case fan is assumed to be 80mm in size. Larger fans such as 120mm will consume slightly more, up to 2.5W.