The Intel 8051 is a Harvard architecture single chip microcontroller (µC) which was developed by Intel in 1980 for use in embedded systems. It was extremely popular in the 1980s and early 1990s, but today it has largely been superseded by a vast range of enhanced devices with 8051-compatible processor cores that are manufactured by more than 20 independent manufacturers including Atmel, Maxim IC (via its Dallas Semiconductor subsidiary), NXP (formerly Philips Semiconductor), Winbond, and Silicon Laboratories. Intel's official designation for the 8051 family of µCs is MCS 51.
Intel's original 8051 family was developed using NMOS technology, but later versions, identified by a letter "C" in their name, e.g. 80C51, used CMOS technology and were less power-hungry than their NMOS predecessors - this made them eminently more suitable for battery-powered devices.