Embedded Systems

1 Define the term embedded system. 2

One mark for each of the following, to a maximum of 2.

• A computer system built into a larger device
• Designed to perform one specific or dedicated task

Model answer. An embedded system is a computer system that is built into a larger device or machine, and it is designed to carry out one specific dedicated task rather than a range of different tasks chosen by the user.

2 Give two examples of embedded systems and, for each, state the task it performs. 4

One mark for each of the following, to a maximum of 4.

• First valid example named, such as a washing machine controller
• Task of the first example stated
• Second valid example named
• Task of the second example stated

Model answer. One example is the controller inside a washing machine, which manages the wash cycle by controlling the water inlet valve, the drum motor speed and the heating element according to the programme the user has selected. A second example is a central heating thermostat, which monitors the temperature reported by a sensor and switches the boiler on or off to keep the room at the target temperature.

3 Explain two advantages of using an embedded system rather than a general purpose computer to control a microwave oven. 4

One mark for each of the following, to a maximum of 4.

• Cheaper to produce because only the hardware needed for the task is included
• Reason linked to the fixed task, such as no need for a screen, keyboard or expansion
• More reliable because the single fixed program can be tested thoroughly and there is less to go wrong
• Smaller and lower power, so it fits inside the appliance and generates little heat

Model answer. The first advantage is cost. Because the system only ever has to run the microwave, the manufacturer can include just the processing power, memory and inputs the task requires, with no monitor, keyboard or expansion slots, so the unit is far cheaper to produce in volume. The second advantage is reliability. The embedded system runs a single fixed program stored in ROM, which can be tested exhaustively before release, and there are far fewer hardware and software components that could fail than in a general purpose computer, so the microwave is much less likely to crash or need maintenance.

4 Describe two differences between an embedded system and a general purpose computer. 4

One mark for each of the following, to a maximum of 4.

• Embedded systems perform one dedicated task, general purpose computers run many different programs
• Embedded software is fixed and usually stored in ROM, general purpose software is installed by the user
• Embedded systems use minimal hardware and have limited interfaces, general purpose computers have full input and output devices
• Embedded systems use less power and are physically smaller

Model answer. The first difference is purpose. An embedded system is built to carry out one dedicated task, such as controlling a set of traffic lights, whereas a general purpose computer such as a laptop is designed to run many different programs chosen by the user. The second difference is how the software is handled. In an embedded system the program is fixed and usually stored in ROM, so it is not intended to be changed by the user, while on a general purpose computer the user installs, updates and removes applications freely. This also means embedded systems need only minimal hardware and a very limited interface, often just a few buttons and lights, whereas a general purpose computer needs a keyboard, a monitor and support for a wide range of peripherals.

5 A manufacturer is deciding whether to control a new coffee machine using an embedded system or a small general purpose computer. Evaluate the use of an embedded system for this purpose. 6

One mark for each of the following, to a maximum of 6.

• Embedded system is cheaper to produce per unit
• Smaller physical size fits inside the machine and uses less power
• More reliable because a single tested program runs on minimal hardware
• Disadvantage: difficult or impossible for the user to update the software
• Disadvantage: no flexibility, the system cannot be repurposed or given new features later
• Reaches a supported conclusion for this specific product

Model answer. An embedded system is a strong choice here. Because a coffee machine only ever needs to run a fixed set of brewing programmes, the manufacturer can specify exactly the processing power, memory and inputs required, which makes each unit significantly cheaper to produce than fitting a general purpose computer. The reduced hardware is also physically smaller, so it fits easily inside the casing, and it draws far less power and generates less heat, which matters in an appliance that already produces heat. Reliability is the strongest argument: a single fixed program running on minimal hardware can be tested exhaustively, and there are far fewer components that could fail, so warranty returns should be low. There are drawbacks. The software is normally stored in ROM, so fixing a bug or adding a new drink option after release may require physically replacing a chip or recalling units, and the system cannot be repurposed for anything else. On balance, because the function of a coffee machine is stable and well defined, and cost and reliability matter far more to the manufacturer than future flexibility, the embedded system is the better choice, provided the design allows firmware to be updated during servicing.