Embedded system is a combination of software and hardware designed and programmed to perform one/more particular task(s). The hardware is designed for specific application and then software is embedded in this hardware to perform the task. Both software and hardware are dedicated to that particular application. The heart of the system is either processor or controller. Processor / controller may be general purpose or special purpose that controls whole system.
There may be more than one processor/controller if system is complex. It may be possible that there is one general purpose processor / controller and one or more special purpose processors / controllers. For example in 3G (or 4G) cell phones there is one general purpose processor that handles user commands, memory and display etc. And there are special purpose processors like DSP for voice communication and network management, display controller to generate real and reach images on color LCD screen.
An embedded system is a special-purpose system in which the computer is completely encapsulated by or dedicated to the device or system it controls. Physically embedded systems range from portable devices such as digital watches and MP3 players, to large stationary installations like traffic lights, factory controllers, or the systems controlling nuclear power plants. In terms of complexity embedded systems can range from very simple with a single microcontroller chip, to very complex with multiple units, peripherals and networks mounted inside a large chassis or enclosure.
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