The megahertz, abbreviated MHz, is a unit of alternating current (AC) or electromagnetic (EM) wave frequency equal to one million hertz (1,000,000 Hz). The megahertz is commonly used to express microprocessor clock speed. The unit is occasionally used in measurements or statements of bandwidth for high-speed digital data, analog and digital video signals, and spread spectrum signals. Other units of frequency are the kilohertz (kHz), equal to 1,000 Hz or 0.001 MHz, and the gigahertz (GHz), equal to 1,000,000,000 Hz or 1,000 MHz.
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An EM signal having a frequency of 1 MHz is near the center of the standard amplitude-modulation (AM) radio broadcast band, and has a wavelength of 300 meters, or about 980 feet. An EM signal of 100 MHz is near the middle of the standard frequency-modulation (FM) radio broadcast band, and has a wavelength of 3 meters, which is a little less than 10 feet. Some radio transmissions are made at frequencies up to many thousands of megahertz.
Typical computer clock speeds, once on the order of a few hundred megahertz, are now often in the low gigahertz range. In designing computer bus architectures, the microprocessor clock speed is considered together with the potential speed or amount of data that can come into the computer from I/O devices in order to optimize overall computer performance.
The hertz as a unit of measure is named after Heinrich Hertz, German physicist.