OCR · GCSE · Computer Science

    Course version: J277 · Version from Sept 2022

    Embedded systems: The purpose and characteristics of embedded systems

    An embedded system is a computer built into another device to control it, rather than being a general-purpose machine used for many tasks.

    Checked against the OCR J277 specification on .

    • Point 1 of 2
    • 4 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    An embedded system is a computer built into another device to control it, rather than being a general-purpose machine used for many tasks. Its purpose is to carry out one dedicated function repeatedly and reliably, often reacting to inputs from sensors. Characteristics include being small, low cost, low power, and having firmware stored in ROM so it starts instantly and cannot easily be changed. For example, a washing machine controller reads temperature and door sensors, then drives the motor and valve. It does not run word processors or games. Because the job is fixed, designers can strip away unnecessary hardware and software, making the system cheap and dependable.

    What earns the marks

    • States that an embedded system is a computer inside another device, dedicated to controlling that device or performing one specific function.
    • Explains that the program is usually held in ROM or flash as firmware, so it is fixed and starts automatically when power is applied.
    • Identifies typical characteristics such as small size, low cost, low power consumption and limited processing or memory resources.
    • Describes interaction with the physical world through sensors and actuators, for example reading a temperature sensor and switching a heater.
    • Contrasts embedded systems with general-purpose computers that run many different applications and can be reprogrammed by the user.

    Common mistakes and how to put them right

    • Saying an embedded system is simply a small computer.

      Put it right: , size is not the defining feature; the defining feature is that it is dedicated to controlling a larger device.

    • Claiming embedded systems always run an operating system with a graphical user interface.

      Put it right: , many run a single program directly with no user interface.

    • Confusing ROM with RAM when describing firmware.

      Put it right: , firmware is normally stored in non-volatile ROM or flash so it survives power loss, while RAM is volatile working memory.

    Exam tips

    • Link each characteristic to a benefit, such as low power use extending battery life in a portable device.
    • Use a named device and describe the input, processing and output to show understanding rather than listing features.
    • When comparing with a general-purpose computer, mention reprogrammability and range of software as the key difference.

    Try the lesson

    The start of the Embedded systems: The purpose and characteristics of embedded systems lesson, made from checked teaching notes for this specification point.

    Have a go first

    What is the main purpose of an embedded system?

    Listen

    An embedded system is a computer built into another device to control it, rather than being a general-purpose machine used for many tasks. Its purpose is to carry out one dedicated function repeatedly and reliably, often reacting to inputs from sensors. Characteristics include being small, low cost, low power, and having firmware stored in ROM so it starts instantly and cannot easily be changed. For example, a washing machine controller reads temperature and door sensors, then drives the motor and valve. It does not run word processors or games. Because the job is fixed, designers can strip away unnecessary hardware and software, making the system cheap and dependable. A strong answer earns marks for these points. States that an embedded system is a computer inside another device, dedicated to controlling that device or performing one specific function. Explains that the program is usually held in ROM or flash as firmware, so it is fixed and starts automatically when power is applied. Identifies typical characteristics such as small size, low cost, low power consumption and limited processing or memory resources. Describes interaction with the physical world through sensors and actuators, for example reading a temperature sensor and switching a heater. A common slip: Saying an embedded system is simply a small computer. Instead, , size is not the defining feature; the defining feature is that it is dedicated to controlling a larger device. Exam tip: Link each characteristic to a benefit, such as low power use extending battery life in a portable device.

    See it

    A top-down flowchart. The top node reads 'Embedded system: computer built into another device'. It branches to four nodes. The first branch leads to 'Purpose: one dedicated function, repeatedly and reliably', which leads to 'Reacts to inputs from sensors', which leads to 'Drives outputs such as motor and valve'. The second branch leads to 'Characteristics: small, low cost, low power'. The third branch leads to 'Firmware stored in ROM', which splits into 'Starts instantly' and 'Cannot easily be changed'. The fourth branch leads to 'Contrast: general-purpose computer runs many applications and can be reprogrammed'.
    Shows the purpose, characteristics and sensor-driven operation of an embedded system, contrasted with a general-purpose computer.

    Key words

    Say what each word means before you turn the card.

    Dedicated function

    Try answering aloud or in your head before turning the card.

    Firmware in ROM

    Try answering aloud or in your head before turning the card.

    Low cost and low power

    Try answering aloud or in your head before turning the card.

    Interaction with sensors and actuators

    Try answering aloud or in your head before turning the card.

    See every definition
    Dedicated function
    The single job an embedded system carries out repeatedly and reliably, rather than being a general-purpose machine used for many tasks.
    Firmware in ROM
    The program stored in ROM so the system starts instantly and cannot easily be changed.
    Low cost and low power
    Characteristics of embedded systems that make the system cheap and dependable, with unnecessary hardware and software stripped away.
    Interaction with sensors and actuators
    Reacting to inputs from sensors and driving parts such as a motor and valve in the physical world.

    Label the diagram

    Some boxes have lost their names. Pick the right name for each number.

    The diagram again, with 3 boxes numbered instead of named. A top-down flowchart. The top node reads 'Embedded system: computer built into another device'. It branches to four nodes. The first branch leads to 'Purpose: one dedicated function, repeatedly and reliably', which leads to 'Reacts to inputs from sensors', which leads to 'Drives outputs such as motor and valve'. The second branch leads to 'Characteristics: small, low cost, low power'. The third branch leads to 'Firmware stored in ROM', which splits into 'Starts instantly' and 'Cannot easily be changed'. The fourth branch leads to 'Contrast: general-purpose computer runs many applications and can be reprogrammed'.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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