Microsecond (µs)
The microsecond is one millionth of a second, a duration so brief that light travels only 300 meters in that time. It occupies a timescale invisible to human perception but essential to modern technology. Radar systems measure the round-trip travel time of radio pulses in microseconds to determine the distance to aircraft. The memory chips in your computer retrieve data from cache in one to ten microseconds. Medical ultrasound devices send and receive sound pulses with microsecond precision to build images of internal organs. The microsecond is the timescale at which much of modern electronics operates, sitting between the nanosecond world of processor logic and the millisecond world of human-facing interfaces.
Definition
One microsecond equals 0.000001 seconds, or 1/1,000,000 of a second. It equals 1,000 nanoseconds. One millisecond contains exactly 1,000 microseconds. One second contains exactly 1,000,000 microseconds.
History
The microsecond became a practical unit of measurement with the development of vacuum tube electronics in the first half of the twentieth century. Early radio engineers needed to describe the duration of transmitted pulses and the propagation delays in circuits, and the second was far too large. Radar development during and after the Second World War made microsecond timing critical: the distance to a target is calculated from the time a radar pulse takes to return, and at radio wave speeds that means measuring intervals of a few to a few hundred microseconds. The development of digital computers in the 1950s and 1960s brought microsecond timing into computing: the first commercial computers had cycle times measured in hundreds of microseconds, and engineers tracked progress in terms of how many microseconds it took to complete basic operations.
Common Uses
Radar systems use microseconds to measure target range. A radar pulse that returns after 6.7 microseconds has traveled one nautical mile. Medical ultrasound imaging sends sound pulses into the body and listens for echoes; the time delay, measured in microseconds, indicates the depth of tissue boundaries. In computing, the latency of DRAM memory is measured in tens of nanoseconds but often approximated in microseconds for higher-level analysis. GPS receivers measure the arrival times of satellite signals with sub-microsecond precision to calculate position. In photography, high-speed electronic flash units have pulse durations of a few microseconds, short enough to freeze the motion of a hummingbird or a bursting water balloon.
Did You Know? Facts About Microsecond
- Light travels exactly 299.792 meters in one microsecond, almost exactly 300 meters. Radio engineers use this to mentally calculate radar distances: a 1-microsecond round trip means the target is 150 meters away.
- The entire Apollo 11 mission computer, which guided astronauts to the Moon and back, had a clock cycle time of about 11.7 microseconds. A modern smartphone processor completes the same cycle in less than a nanosecond.
- Lightning strikes last about 200,000 microseconds in total, but the visible return stroke, the bright flash you see, lasts only about 70 microseconds.
- The human nervous system transmits signals at speeds of roughly 70 meters per second, meaning a nerve signal takes about 14 microseconds to travel one millimeter. A reflex arc from foot to spinal cord takes about 20,000 microseconds.
- Wi-Fi signals travel through the air at nearly the speed of light. The round trip from your device to a router one meter away takes about 6.7 nanoseconds, but processing delays in the hardware add hundreds of microseconds.