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A megahertz (MHz) is one million (106) hertz, a measure of frequency.

In radio, most frequencies fall into the MHz range:

A common alternative means of describing a radio frequency is using its wavelength, though since the adoption of the hertz as an SI unit, this is becoming rare.

In computing, most CPUss are labelled in terms of megahertz. This refers to the cycle frequency of the CPU's "master" clock. If two otherwise identical CPUs have different "clock speeds", the one with the higher clock speed (larger megahertz) will be faster than the other. In practice, many other factors influence the performance of computers, and consumers are advised to place little store on this factor when purchasing a computer - if performance is important, more detailed information than a MHz rating is required to make an informed decision. See benchmark for further discussion of computer performance comparisons.

Note: many computers now have clock frequencies above 1000 MHz, and their clock frequencies are now quoted in gigahertz (109 hertz): so an 1800 MHz clock frequency is referred to as 1.8 GHz.

See also: hertz, kilohertz (1000 hertz), terahertz (1012 hertz), and petahertz (1015 hertz), SI prefixes