Understand the concept of an embedded system and what embedded systems are…

The idea

An embedded system is a computer built into a larger device to carry out one dedicated job, rather than being a general-purpose machine you program for many tasks. Its program is usually stored in ROM or flash memory and runs automatically when the device is switched on, so the user does not install software or choose what it does. The processor, memory and input/output are chosen and fixed for that single function, which keeps the unit small, cheap, low-power and reliable. Typical uses include washing machines controlling wash cycles, microwave ovens timing cooking, car engine management adjusting fuel and ignition, central heating thermostats sensing temperature, and traffic lights sequencing signals. Because the function is fixed, embedded systems are assessed by matching a described device to its dedicated purpose and explaining why it is embedded rather than general-purpose.

What earns the marks

• Defines an embedded system as a computer dedicated to one specific function within a larger device.
• States that its program is typically held in ROM or flash memory and starts automatically.
• Explains that the user cannot normally install other software or repurpose the device.
• Identifies that processor, memory and input/output are fixed and chosen for the single task.
• Links the design to benefits such as small size, low cost, low power use or reliability.
• Gives a valid example such as a washing machine, microwave, car engine management unit, thermostat or traffic light controller and names its dedicated job.

Common mistakes and how to put them right

• Thinking any small computer is embedded.

  Put it right: An embedded system is defined by its single dedicated function inside a host device, not by physical size.

• Believing embedded systems run a full general-purpose operating system with user-installed apps.

  Put it right: Their firmware is fixed and runs one task automatically.

• Confusing an embedded system with a desktop PC used for many tasks.

  Put it right: A general-purpose computer can run many different programs chosen by the user, while an embedded system cannot.

• Assuming embedded systems have no processor or memory.

  Put it right: They contain a processor and memory, but these are selected and fixed for the dedicated job.

Exam tips

• Read the question stem to see whether it asks for a definition, a purpose or an example, and answer only that.
• When giving an example, name both the device and the specific job it controls, for example a washing machine controlling wash cycles.
• Eliminate options that describe general-purpose computers or user-installed software, because these contradict the embedded concept.