nanosecond (ns or nsec)

What is a nanosecond (ns or nsec)?

A nanosecond (ns or nsec) is one-billionth (10^-9) of a second. A nanosecond is a measure of time that has many practical applications, particularly in computer science and IT. The term nano comes from the Greek root nanos, which means dwarf.

One nanosecond (ns) represents the time required to perform one full cycle of a 1 gigahertz (GHz) signal. That is, 1/(1^-9 sec) is 1,000,000,000 hertz (Hz). Most current computer processors use a clock signal well above 1 GHz. For example, the Intel Core i9-13900K processor uses a base clock frequency of 3 GHz, which completes a single clock cycle in 1/3,000,000,000 Hz or 0.333^-9 ns -- roughly one-third of one nanosecond.

Nanosecond time scales are also common in associated computer hardware devices such as RAM (random access memory) read and write access times. The nanosecond rating determines the speed and latency of the RAM and significantly impacts the computer system's performance.

At one-billionth of a second, a nanosecond is smaller than a millisecond and microsecond, but larger than a picosecond, femtosecond, attosecond or zeptosecond. Computer memory speed is often represented in nanoseconds. A lower-memory nanosecond specification means the computer can access its memory faster and generally operate at a higher speed to produce its output. Thus, RAM that operates at 60 ns is slower -- and usually less desirable -- than RAM that operates at 20 ns.

Nanosecond vs. other time measurements

A nanosecond is only one time measurement scale. There are many measures available that are slower -- and faster -- than nanoseconds.

In terms of slower (longer) measurements, a second is the smallest unit of time as represented on a watch or clock. A millisecond is one-thousandth of a second (10^-3). It's written as ms or msec and is commonly used to measure the time required to read to or write from a hard disk or solid-state drive and to measure the travel time of data packets on the internet. A microsecond is one-millionth (10^-6) of a second and is represented as μs (Greek letter mu plus s). The nanosecond comes next at one billionth (10^-9) of a second.

The scientific community also has many faster (shorter) time measurements available. A picosecond (ps) is one-trillionth (10^-12) of a second or one-millionth of a microsecond. A femtosecond (fs) is one-quadrillionth of a second (10^-15) or one-millionth of a nanosecond, and an attosecond is one-quintillionth (10^-18) of a second. The femtosecond is sometimes used in laser technology, while the attosecond is used in photon research. The zeptosecond (zs) is one sextillionth (10^-21) of a second -- or roughly the time needed for a photon of light to cross the distance of a single hydrogen molecule.

There are several faster (shorter) time scales available, including the yoctosecond (ys or 10^-24), rontosecond (rs or 10^-27) and quectosecond (qs or 10^-30). However, such time scales are so short that they're difficult to express in practical terms and are typically related to fields such as experimental physics.

Latency and nanoseconds in RAM

For computer RAM, latency is usually measured in nanoseconds. Latency is a combination of speed and Column Address Strobe (CAS) latency. It can be calculated by multiplying clock cycle duration by the total number of clock cycles. System performance is affected by both speed and latency, so increasing the former and decreasing the latter can result in better performance.

CAS latency (CL) measures the total number of clock cycles the data must go through; that is, the number of clock cycles it takes for RAM to access the data -- called by the CPU -- in one of its columns and make it available on its output pins. A RAM module's latency is determined by CL and the duration of each clock cycle, which is measured in nanoseconds.

A module's latency in terms of nanoseconds enables comparisons between modules. Specifically, it shows whether one module is more responsive than another. For example, a single data rate (SDR) module with a clock cycle time of 8 ns and CL of 3 has a total latency of 24 ns. In comparison, a double data rate 5 (DDR5) module with a clock cycle time of 0.42 ns and CL of 40 has a total latency of only 16.67 ns. Since DDR5 has lower latency, it indicates that it's more responsive than the SDR memory.

As memory technology has improved, clock cycle times have decreased, and therefore, overall processing speeds have increased. But, at the same time, the CL values have also increased. Combining these two factors means that the true RAM latency as measured in nanoseconds has remained roughly the same.

That said, it's possible to improve system performance by using newer, faster and more efficient memory; for example, upgrading from a computer with DDR4 memory to a system with DDR5 memory. The key is to maintain a balance between the maximum speed the processor is capable of and the lowest latency memory available within a user's budget.

Nanoseconds, electricity and light

A nanosecond is sometimes referred to as a light foot, since light can travel approximately 1 foot -- 11.8 inches -- in 1 ns. Electricity also travels about 1 foot in 1 ns. Rear Admiral Grace Hopper is famous for demonstrating this phenomenon by handing out foot-long lengths of wire to those who attended her lectures on technology to illustrate how far an electrical signal can travel in 1 ns. Since the wire is a tangible object, it helps to show the difficult-to-comprehend concept of a billionth of a second in more tangible terms.

What is a nanosecond laser?

A nanosecond laser, also known as a nanolaser, is a type of Q-switched pulsed laser. Q-switching, also known as Q-spoiling or giant pulse formation, is a laser technique that produces a pulsed output beam with extremely high peak power and lower pulse repetition rates. The pulses are generated using a high-speed shutter.

The depletion time for gain materials used in the laser is usually a few nanoseconds, which results in the generation of light pulses. Many lasers that can be Q-switched can be used to produce nanosecond pulse width lasers. These include solid-state lasers, flash lamp lasers, fiber lasers and microchip lasers. Nanosecond lasers are available in many wavelength ranges -- ultraviolet to infrared -- as well as pulse energies from nanojoule to joule and repetition rates from hertz to megahertz.

These lasers are commonly used in applications that demand high intensities in nanosecond pulses, such as metal cutting, laser-induced breakdown spectroscopy and material marking.

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