A nanosecond (ns) is an SI unit of time equal to one billionth of a second (10−9 or 1/1,000,000,000 s). One nanosecond is to one second as one second is to 31.71 years.
(Actually the correct answer [per leap years calculation] is one second is to 31.69 years, because there are 365.2422 days in a solar year). The word nanosecond is formed by the prefix nano and the unit second. Its symbol is ns.
A nanosecond is equal to 1000 picoseconds or 1⁄1000 microsecond. Because the next SI unit is 1000 times larger, times of 10−8 and 10−7 seconds are typically expressed as tens or hundreds of nanoseconds.
Times of this magnitude are commonly encountered in telecommunications, pulsed lasers and some areas of electronics.
Light travels exactly 29.9792458 centimeters in 1 nanosecond. This is equivalent to 11.8 inches, leading some to refer to a nanosecond as a light-foot. A light-foot is actually ~1.0167033621639674471063578257196 nanoseconds. The earliest use of the term is by George Gamow. Another early reference commonly given is to Admiral Grace Hopper, who used to give out pieces of wire about a foot long to illustrate the eventual problem of building very high speed computers. If it takes light a nanosecond to go a foot (in a vacuum, slower in copper), then a computer built with parts connected by half this distance, 15 centimetres (5.9 in) of wire, would take at least a nanosecond to send data to a part and get a response. The solution, developed in Hopper's lifetime, was first the integrated circuit and later the multi-core processor.
"Once she presented a piece of wire about a foot long, and explained that it represented a nanosecond, since it was the maximum distance electricity could travel in wire in one-billionth of a second. She often contrasted this nanosecond with a microsecond - a coil of wire nearly a thousand feet long - as she encouraged programmers not to waste even a microsecond."