Encyclopedia of Computer Science and Technology

178 employment in the computer fieldBecause available memory is limited, embedded programcode tends to be compact. Since embedded systems areoften responsible for critical infrastructure, their operatingprograms must be carefully debugged. Designers tryto make programs “robust” so they can respond sensiblyto unexpected conditions or at least “fail gracefully” ina way least likely to cause damage. Other strategies toimprove the reliability of embedded systems include theuse of overdesigned, fault-tolerant components (as in themilitary “milspec”) and the use of separate, redundantsystems so that a failing system can be “locked out” andprocessing can continue elsewhere.An embedded system is a computer processor that is part of a“real-world” device that must interact with its environment. Sensorinputs (such as torque or pressure sensors) provide real-time dataabout conditions faced by the device (such as a vehicle). This datais processed by the onboard processor under the control of a permanent(ROM) program, and commands are issued to the effectorcontrols, which might, for example, apply braking pressure.such as medical monitoring systems and power transmissionnetworks. (The potential vulnerability of embedded systemsto the Y2K date-related problems was a major concern inthe months leading up to 2000, especially because manyembedded systems might have to be replaced rather thanjust reprogrammed. In the event, it turned out that therewere relatively few date-dependent systems and only minordisruptions were experienced. See y2k problem.)Characteristics of Embedded SystemsWhat most distinguishes an embedded system from a desktopcomputer is not that it is hidden inside some other device,but that it runs a single, permanent program whose job it isto monitor and respond to the environment in some way.For example, an oven controller would accept a user input(the desired temperature), monitor a sensor or thermostat,and control the heat to ensure that the correct temperatureis being maintained. Embedded systems are thus similar torobots in that they sense and manipulate their environment.Architecturally, an embedded system typically consists ofa microprocessor, some nonvolatile memory (memory that canmaintain its contents indefinitely), sensors (to receive readingsfrom the environment), signal processors (to convertinputs into usable information), and “effectuators” (switchesor other controls that the embedded system can use to changeits environment). In practice, an embedded system may nothave its own sensors or effectors, but instead interface withother systems (such as avionics or steering).Programmers of embedded systems often use specialcompilers or languages that are particularly suitedfor creating embedded software (see ada and forth).Further ReadingCatsoulis, John. Designing Embedded Hardware. 2nd ed. Sebastapol,Calif.: O’Reilly, 2005.Embedded.com: “Thinking inside the Box.” Available online. URL:http://www.embedded.com/. Accessed July 22, 2007.Embedded Systems. Dr. Dobb’s Portal. Available online. URL:http://www.ddj.com/dept/embedded/. Accessed July 22, 2007.Norergaard, Tammy. Embedded Systems Architecture: A ComprehensiveGuide for Engineers and Programmers. Burlington, Mass.:Newnes/Elsevier, 2005.Simon, David E. An Embedded Software Primer. Upper Saddle River,N.J.: Addison-Wesley/Pearson Education, 1999.employment in the computer fieldThe number of computer-related positions has grown rapidlyover the past few decades. According to the U.S. Bureauof Labor Statistics, by the mid-1990s the fastest-growingprofessions in the United States included systems analysts,computer scientists, and computer engineers. By the mid-2000s, computer-related occupations were still near the topof the list, which by then also included network and communicationsanalysts (second only to “home health aids”).Computer-related employment can be broken down intothe following general categories:• hardware design and manufacturing, including computersystems, peripherals, communications and networkhardware, and other devices• the software industry, ranging from business applicationsto consumer software, games, and entertainment• the administrative sector (systems administration,network administration, database administration,computer security, and so on)• the Web sector, including ISPs, Web hosts and pagedevelopers, and e-commerce applications• the support sector, including training and education,computer book publishing, technical support, andsystems repair and maintenanceIn addition to these “pure” computer-related jobs, thereare many other positions that involve working with PCs.These include word processing/desktop publishing, statistics,scientific research, accounting and billing, shipping,retail sales and inventory, and manufacturing. (See alsoprogramming as a profession.)