Power consumption of a computer can be an issue both for people interested in reducing environmental impacts from electrical use and for people who are simply trying to reduce a monthly power bill. When looking for ways to cut electricity use, comparing laptop computer power consumption to desktop computer power consumption shows that a laptop computer will use much less power than a desktop computer.
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Monitor Power Consumption
Power consumption from a monitor built in to a laptop computer is included in overall laptop power consumption statistics. For example, if a laptop uses 40 watts of power during use, that total includes the power needed by the monitor. If a desktop uses 110 watts of power during use, that total does not include the monitor. If a monitor uses 80 watts of power, the total power consumption of the desktop plus monitor would be 190 watts, or nearly five times the power consumption of the laptop. External monitors for desktop computers use between 35 watts, for some 17 inch LCD monitors, to 80 watts for many 17 inch CRT monitors.
Power Consumption When Off
Even when turned off, computers use power when plugged in to the wall. Most desktops use between 1 and 2 watts of power when turned off and plugged in to the wall. Laptops use between 1 and 3 watts when left plugged in with a fully charged battery. But when turned off and plugged in to charge the battery, a laptop can use between 30 and 70 watts until the battery is fully charged and the computer's charging mechanism switches off.
Boot Power Consumption
Most computers use more power while booting than during normal use. This is because during boot, almost all computer subsystems are used. The hard disk is accessed frequently, the monitor is on, and the CPU is under relatively heavy use as the operating system loads and initialises. Power consumption during boot on laptops can range from 21 watts to 59 watts. Power consumption in desktops can range from 105 watts to 280 watts, including the monitor.
Power Consumption Under Load
Under load, performing common computing tasks like word processing and Web browsing, power consumption in laptops can range from 19 watts to 58 watts. Desktop power usage, including the monitor, can range from 100 watts to 260 watts. But in server-class desktop computers with larger power supplies and more installed components, power consumption can sometimes be higher.
Power Consumption in Sleep Mode
A computer in sleep mode uses about twice the power as a computer that is off. Sleep mode is a low power consumption mode where most of the computer subsystems are turned off. Sleep mode requires some power to maintain memory and occasionally power the computer up to perform scheduled tasks. But on average, computers in sleep mode use much less power than an unused computer that is left on. Sleep mode on laptops uses between 1 and 4 watts. Sleep mode on desktops uses between 1 and 5 watts.
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