Look up nanosecond in Wiktionary, the free dictionary.
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 31.7 years.
The word nanosecond is formed by the prefixnano and the unitsecond. Its symbol is ns.
A nanosecond is equal to 1000 picoseconds or 1⁄1000microsecond. 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.
Light travels approximately 29.9 centimeters in 1 nanosecond. This is equivalent to 11.8 inches, leading to some to refer to a nanosecond as a light-foot. The earliest 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. "
Light travels ~29.979 cm in one nanosecond, meaning that, technically, a light-foot is ~1.0167 nanoseconds.