Power-Use Calculations

When expanding or upgrading your PC, ensure that your power supply is capable of providing sufficient current to power all the system’s internal devices. One way to see whether your system is capable of expansion is to calculate the levels of power consumption by the various system components in your system, and then compare that to the rating on the power supply to see if it is up to the job. This calculation can also help you decide whether you must upgrade the power supply to a more capable unit. Unfortunately, these calculations can be difficult to make accurately because many manufacturers do not publish detailed power consumption data for their products. In some cases, you can find the specs from a similar component and go by that data instead. Usually components of the same basic design, capability, and vintage have relatively the same power consumption characteristics. Table 18.26 shows the range of power usage for typical PC components I’ve observed over the past few years.

Table 18.26. Power Consumption Calculation

Component	Power Usage	Comments
Motherboard	50W–75W	Depends on the number of integrated components.
Processor	25W–150W	For each physical processor (not cores). Most are 50W–100W.
RAM	5W–15W	For each module (DIMM).
Integrated video	5W–15W	Integrated into the North Bridge chip.
Discrete video card	25W–300W	For each video card.
PCI card	5W–15W	For each nonvideo card.
PCIe card	10W–25W	For each nonvideo card.
Hard disk drive	15W–30W	For each drive. Power use increased during startup.
Optical drive	15W–35W	For each drive.
Cooling fan	3W–5W	For each fan.
USB/FireWire	2W–5W	For each used port.