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Home -> Resources -> Twenty-One Green IT Tips -> 13. Run CPUs at Slower Clock Speeds
13. Run CPUs at Slower Clock Speeds Did you know that a faster CPU also uses more power? You can reduce the amount of power you use by reducing your CPU speed. To figure out exactly how much power, you can use a power meter to measure power usage (see Tip 2). Our Tests In one set of tests, we got an average of 10 watts saved every time we slowed down the clock speed by 400 MHz. Our test system had an ASUS motherboard and an AMD 2800+ processor. At clock speeds of 2083 MHz (2.083 GHz), the system required 135 watts of power. When we slowed the clock speed to 1667 MHz (1.667 GHz), the power required dropped to 126 watts. At the slowest speed, 1250 MHz (1.25 GHz), the power required was 115 watts. Translating the Savings to Dollars While 20 watts of savings might not seem a lot, but you might be wondering the benefit in "real" terms. If such a system were kept on 24x7 for an entire year (which is 8760 hours), the 20 watts of savings would translate into 175 kilowatt hours. According to the Department of Energy, the average price that was paid in the United States for electricity was 11.28 cents per kilowatt hour. Given these factors, the net savings for a year is $19.74. In other words, every watt saved is equal to one dollar ($1.00) saved for a machine that is left on full-time. Since server systems are often kept running all the time, modifying the CPU speed makes a lot of sense. (And it saves more than a few cents!) Intel SpeedStep Technology If you can save power by running a CPU slower, why doesn't everyone do this? It turns out that Intel has a technology that does this. The technology is called Enhanced Intel SpeedStep(R) Technology (EIST). The requirements for EIST are too numerous to list here, so click here to find more details on the Intel website. Web search:  CPU power consumption
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