Megahertz

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

In radio, many frequencies fall into the MHz range:

LF (Low Frequency) 0.03 - 0.3 MHz
MF (Medium Frequency) 0.3-3 MHz
HF (High Frequency) 3-30 MHz
VHF (Very High Frequency) 30 - 300 MHz
UHF (Ultra High Frequency) 300 - 1000 MHz

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. Wavelength varies inversely to frequency, i.e., high frequencies are associated with short wavelengths.

In computing, most CPUss made between 1974 and 2000 were labelled in terms of megahertz (though modern computers have processor speeds in the Gigahertz (10⁹ hertz) range). The number of megahertz refers to the cycle frequency of the CPU's master clock.

It is often assumed that if two otherwise identical CPUs have different "clock speeds", the one with the higher clock speed will be faster than the other. However, in practice, many other factors influence the performance of computers, and consumers are advised to take in other factors when purchasing a computer.

For example, a RISC processor, which has very small instructions that can be accomplished quickly, may run at a higher clock rate (at higher MHz) than a CISC processor with large instructions, but because the CISC processor accomplishes more during each clock, it may be faster for any real-world application. 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.

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