An enormous and growing number of computers today fall in the category of embedded systems. Multiple processors, microcontrollers and dedicated computers manage multiple aspects of modern life, and outnumber by far the "traditional computers" or home-PCs that have invaded many homes and most workplaces around the world. (Most PCs, in fact, contain a great number of embedded systems within).
The largest share of embedded systems are very simple and cheap microcontrollers, that contain within a chip their (usually small) program memory (in ROM or Flash), working memory or registers (RAM), and their input/output (I/O) subsystems. The end user rarely knows of (or modifies) the components or the internal program of an embedded system. The best systems perform their functions consistently and absolutely unobtrusively. A tipical case is the controller within a standard PC keyboard (derived from the venerable 8048 Intel family), that permanently scans at great speed for pressed keys,and their sequences, generating "scan codes" which are converted to a serial stream of bits and sent to another controller (derived from the 8042 family) sitting on most PC motherboards since the first IBM AT models. In growing degree of complexity, we could also point out the ever-more-sophisticated hard disk controllers, and the 32bit processors moving the ropes within most laser printers. Last but not least, a modern car deploys dozens of controllers in uses ranging from injection and fuel mixture ,braking ABS, to cockpit ambient temperature. Increasingly, the issue in complex systems such as cars is moving information around between controllers reliably and with no quirks. Enourmous effort is being devoted to networking systems (eg. CAN) for microcontrollers and industrial applications.
Many problems, specially those that imply repetitive sequences withing machines or control panels, can be resolved using PLCs (Programmable Logic Controllers). These are in turn embedded systems but their I/O is configurable, and their logic can be programmed by the user. Many PLCs use a programming system called ladder logic, inherited from the days of relay logic. The more recent models are very simple to manage, and can be programmed from a PC or Notebook. Most include additional high level language support.
Still, embedded systems are hard to beat in cost, size and power consumption, and their applications are infinitely expanding.
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