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.
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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 are constantly increasing, but generally are on the order of a few hundred megahertz.
The bandwidth of a digital signal, in megahertz, is related to the data speed in bits per second. In general, the greater the data speed, the larger the bandwidth. Data speed is not, however, the same thing as bandwidth. A high-speed cable or fiberoptic modem operating at a speed of 5,000,000 bps has, in a certain sense, a nominal frequency of 5 MHz. But the bandwidth is generally much smaller, because it depends on variations in the individual data elements, not on the number of data bits per unit time.