The Intel MCS-51 (commonly referred to as 8051) is a Harvard architecture, single chip microcontroller (µC) series which was developed by Intel in 1980 for use in embedded systems. Intel's original versions were popular in the 1980s and early 1990s. While Intel no longer manufactures the MCS-51, binary compatible derivatives remain popular today. In addition to these physical devices, several companies also offer MCS-51 derivatives as IP cores for use in FPGAs or ASICs designs.

Intel's original MCS-51 family was developed using NMOS technology, but later versions, identified by a letter C in their name (e.g., 80C51) used CMOS technology and consumed less power than their NMOS predecessors. This made them more suitable for battery-powered devices.

The 8051 architecture provides many functions (CPU, RAM, ROM, I/O, interrupt logic, timer, etc.) in a single package

One particularly useful feature of the 8051 core was the inclusion of a boolean processing engine which allows bit-level boolean logic operations to be carried out directly and efficiently on select internal registers and select RAM locations. This advantageous feature helped cement the 8051's popularity in industrial control applications because it reduced code size by as much as 30%. Another valued feature is the inclusion of four bank selectable working register sets which greatly reduce the amount of time required to complete an interrupt service routine. With a single instruction the 8051 can switch register banks as opposed to the time consuming task of transferring the critical registers to the stack or designated RAM locations. These registers also allowed the 8051 to quickly perform a context switch which is essential for time sensitive real-time applications.

Coordinates: 37°23′16.54″N 121°57′48.74″W / 37.3879278°N 121.9635389°W / 37.3879278; -121.9635389

Intel Corporation (NASDAQ: INTC) is an American multinational semiconductor chip maker corporation headquartered in Santa Clara, California, United States and the world's largest and highest valued semiconductor chip maker, based on revenue. It is the inventor of the x86 series of microprocessors, the processors found in most personal computers. Intel Corporation, founded on July 18, 1968, is a portmanteau of Integrated Electronics (though a common misconception is that "Intel" is from the word intelligence^{[citation needed]}). Intel also makes motherboard chipsets, network interface controllers and integrated circuits, flash memory, graphic chips, embedded processors and other devices related to communications and computing. Founded by semiconductor pioneers Robert Noyce and Gordon Moore and widely associated with the executive leadership and vision of Andrew Grove, Intel combines advanced chip design capability with a leading-edge manufacturing capability. Though Intel was originally known primarily to engineers and technologists, its "Intel Inside" advertising campaign of the 1990s made it and its Pentium processor household names.