What is an embedded system ?

An embedded system is some combination of computer hardware and software, either fixed in capability or programmable, that is specifically designed for a particular kind of application device. Industrial machines, automobiles, medical equipment, cameras, household appliances, airplanes, vending machines, and toys as well as the more obvious cellular phone and PDA are among the myriad possible hosts of an embedded system. Embedded systems that are programmable are provided with a programming interface.

Another definition: Any electronic system that uses a CPU chip, but that is not a general-purpose workstation, desktop or laptop computer. Such systems generally use microprocessors, or they may use custom-designed chips or both. In embedded systems, the software typically resides in firmware, such as a flash memory or ROM chip, in contrast to a general-purpose computer that loads its programs into RAM each time. Sometimes, single board and rack mounted general-purpose computers are called "embedded computers" if used to control a single printer, drill press or other such device.

A third definition: Hardware and software which forms a component of some larger system and which is expected to function without human intervention. A typical embedded system consists of a single-board {microcomputer} with software in {ROM}, which starts running some special purpose {application program} as soon as it is turned on and will not stop until it is turned off (if ever). An embedded system may include some kind of {operating system} but often it will be simple enough to be written as a single program. It will not usually have any of the normal {peripheral}s such as a keyboard, monitor, serial connections, mass storage, etc. or any kind of user interface software unless these are required by the overall system of which it is a part.