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

Megahertz in radio

When used in the context of radio, MHz refers to the number of oscillations of electromagnetic radiation per second. Several parts of the radio spectrum 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

The HF, VHF, UHF references are something of a misnomer: most radiocommunications today occur at higher frequencies due to congestion in the lower frequency bands. Experts in the field of radiocommunications classify these other categories of spectrum by bands. The names of these bands are idosyncratic, but are used often in radiocommunications.

  • L-Band 1-2 GHz (1000 MHz = 1 gigahertz GHz)
  • S-Band 2-4 GHz
  • C-Band 4-8 GHz
  • X-Band 8-12 GHz
  • Ku-Band 12-18 GHz
  • K-Band 18-27 GHz
  • Ka Band 27-40 GHz
  • V-Band 40-75 GHz
  • W- Band 75-110 GHz

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.

Megahertz in computing

Most CPUs 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 frequency of the CPU's master clock signal ("clock speed").

Various computer busses, such as memory busses connecting the CPU and system RAM, also transfers data using clock signals operating at frequencies in the megahertz range. The operating frequency of computer busses is sometimes adverticed by computer sellers, though not as often as the CPU frequency.

It is often assumed that if two CPUs have different "clock speeds", the one with the higher clock speed will perform better than the other. However, while clock speed is an important factor in overall performance, many other factors influence the performance of computers, and a better comparison is archived by using benchmarks.

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

See also

kilohertz << megahertz << gigahertz

Last updated: 08-17-2005 06:48:55
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