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CPU Architecture and the Fetch–Decode–Execute Cycle: Question 4

Syllabus 3.1

Structured 7 marks

A rice cooker contains a single microprocessor running one program stored permanently in its memory. A temperature sensor tells the microprocessor when the rice and water inside have reached boiling point, and the microprocessor then automatically switches the cooker from "cook" mode to "keep warm" mode. The owner cannot reprogram this microprocessor to run any other software.

(a) State what is meant by an embedded system. [1]

(b) Explain two reasons, based on the description above, why the rice cooker's microprocessor should be classed as an embedded system rather than as a general purpose computer. [4]

(c) A different kitchen device, a recipe tablet, can run a recipe app, a web browser and a video-calling app, and its owner can install further apps from an app store. State, with a reason, whether this tablet should be classed as an embedded system or a general purpose computer. [2]

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Worked solution

Part (a): Defining an embedded system

An embedded system is a computer system that is built into a larger device to carry out one specific, dedicated function. It is controlled by a microprocessor that runs a single, fixed program rather than software that a user chooses and installs themselves. [1]

Part (b): Applying the definition to the rice cooker

Two distinct reasons can be drawn from the scenario:

  • Dedicated function. The rice cooker’s microprocessor does one job: reading the temperature sensor and switching between cook mode and keep-warm mode. A general purpose computer, by contrast, is designed to be used for many different, unrelated tasks. [2]
  • Fixed, non-reprogrammable software. The program is stored permanently and the owner cannot install different software to make the microprocessor do something else, unlike a general purpose computer such as a PC or laptop, which is designed to run whatever application software the user chooses to install. [2]

Part (c): Classifying the recipe tablet

The recipe tablet is not an embedded system. It should be classed as a general purpose computer. [1] The key reason is that it runs several unrelated applications (a recipe app, a web browser, a video-calling app) and its owner can install further apps of their choosing, which is exactly the flexible, multi-purpose, user-installable software behaviour that distinguishes a general purpose computer from an embedded system. [1]

Final answers

  • (a) An embedded system is built into a device to perform one dedicated function, running a single fixed program.
  • (b) The rice cooker’s microprocessor performs only one dedicated function (temperature monitoring and mode switching) and runs a single fixed program the owner cannot change.
  • (c) The recipe tablet is a general purpose computer, because it runs multiple installable applications rather than one dedicated function.