Conversion from Gigahertz to Hertz

Information about the Gigahertz (GHz)

The gigahertz is a unit of frequency equal to one thousand million hertz. Its symbol is GHz. It is the range of modern wireless communication and of the clock inside every current computer, and almost nothing in it was in everyday use before the 1990s.

Wi-Fi occupies two main bands, at 2.4 and 5 gigahertz, with a newer band near 6. The 2.4 gigahertz band is crowded because it is licence-free almost everywhere and shared with Bluetooth, cordless phones and microwave ovens, which operate at 2.45 gigahertz because water molecules absorb energy efficiently there. The 5 gigahertz band offers more channels and higher rates but is absorbed more strongly by walls, so it covers a smaller area.

Mobile telephony spans the range. Earlier generations used bands below 1 gigahertz for their long reach into buildings and across countryside, while newer allocations at 1.8, 2.6 and 3.5 gigahertz carry more data over shorter distances. The higher a frequency, the more bandwidth is available and the less it penetrates, and every generation of network design is a negotiation between those two facts.

Computer clock speeds crossed into gigahertz around the year 2000 and stalled near four a few years later. The limit is thermal: power dissipation rises steeply with frequency, and beyond about four gigahertz a conventional silicon processor cannot shed the heat. Performance gains since then have come from adding cores, widening instruction issue and improving memory hierarchies rather than from raising the clock.

Satellite links, radar and radio astronomy all work here. Weather radar typically runs between 2.7 and 5.6 gigahertz, air traffic control radar in similar bands, and the microwave background radiation that fills the universe peaks near 160 gigahertz, well above the range of terrestrial communication.

Millimetre-wave systems at 24 gigahertz and above are used for automotive collision-avoidance radar and for the highest-capacity mobile network bands. Their very short wavelengths allow small antennas and enormous data rates but are blocked by almost anything, including rain and foliage.

One gigahertz equals one thousand million hertz, 1000 megahertz, or 0.001 terahertz.

Information about the Hertz (Hz)

The hertz is the SI unit of frequency, equal to one cycle per second. Its symbol is Hz. It is a derived unit whose dimension is simply one divided by time, so a quantity in hertz counts how many times something repeats in a second.

It is named after Heinrich Hertz, who between 1886 and 1889 produced and detected radio waves in the laboratory and so confirmed Maxwell's prediction that light and electromagnetic waves are the same phenomenon. The unit was adopted internationally in 1960, replacing the older and more literal cycles per second, which is still occasionally seen on vintage equipment.

Sound occupies the low end of the scale. Human hearing runs from roughly 20 hertz to 20,000 hertz, though the upper limit falls with age and is usually well below 16,000 hertz by middle life. Musical pitch is frequency: the A above middle C is fixed at 440 hertz by convention, and each octave is a doubling, so the same note an octave higher is 880 hertz.

Mains electricity alternates at 50 hertz across most of the world and 60 hertz in North America and parts of Japan and South America. The split is historical rather than technical, dating from competing equipment standards in the late nineteenth century, and it is why appliances and clocks that depend on mains frequency cannot simply be moved between regions.

Screens and computing use it constantly. A display refreshing at 60 hertz redraws sixty times a second, and higher rates reduce visible motion blur. Processor clock speeds, once quoted in megahertz and now in gigahertz, count the same thing: how many times per second the internal clock ticks.

The unit also applies to anything periodic that is not a wave. Heart rate at 60 beats per minute is one hertz, a pendulum with a one-second period swings at one hertz, and the frequency of a rotating shaft in revolutions per second is expressed identically.

One hertz equals one cycle per second, 1000 millihertz, or one thousandth of a kilohertz.