Embedded Systems
What Is an Embedded System?
An embedded system is a computer built into a larger device to carry out one dedicated function. Unlike a laptop, you do not sit down and type at it — it sits hidden inside a product, quietly controlling how that product works. A washing machine is a good example: a small computer inside it reads the buttons you press, then switches the water, drum motor and heater on and off in the right order to run your chosen wash. That computer only ever runs the washing programme. It cannot browse the web, play games or run a word processor, because it was designed to do one job and do it well.
An embedded system is a computer that is part of a larger device and is designed to perform a single dedicated task, such as controlling a washing machine or a microwave.
What Is Inside an Embedded System?
At the heart of most embedded systems is a microcontroller — a single chip that combines a processor, a small amount of memory and input/output connections in one package. Putting everything on one chip keeps the device small and cheap. The program the microcontroller runs is called firmware, and it is usually stored in read-only memory so that it is ready the moment the device is switched on and is not lost when the power is turned off.
Because the device only has to do one job, designers give it just enough processing power and memory to do that job — no more. A microwave’s controller does not need the power of a desktop PC, so fitting a large, expensive processor would only waste money and energy. This ‘just enough’ approach is one of the main reasons embedded systems are so cheap to make in huge numbers.
On a laptop you install and delete programs all the time — software is meant to change. Firmware is different: it is written once for the device and normally stays the same for the product’s whole life. Some modern products, such as smart TVs and routers, do let their firmware be updated to fix bugs or add features, but for most simple appliances the firmware is fixed and the user never changes it.
Typical Characteristics
Embedded systems share a recognisable set of features. They are dedicated to one task, small enough to fit inside another product, low-powered so they run cool and cheaply, and low-cost because they are produced in huge numbers. They are also built to be reliable: a pacemaker or a car braking system must work perfectly every time, so the hardware and firmware are kept simple and thoroughly tested.
Many embedded systems are also real-time systems, meaning they must respond to inputs straight away rather than after a delay. When a car’s anti-lock braking system senses a wheel starting to lock, it has to react in a fraction of a second — a late response would be useless. Reacting instantly and predictably is often more important for these systems than raw processing speed.
Typical embedded systems are dedicated to one function, small, low-cost, low-power and highly reliable — and many must respond in real time.
Using an embedded system instead of fitting a full computer brings clear benefits. Because the hardware only does one job, it can be made smaller, cheaper and more energy-efficient, and there is less that can go wrong, so it is more reliable. The trade-off is flexibility: an embedded system cannot easily be upgraded or given new tasks, and if the firmware has a fault it can be hard to fix once the product has been sold.
Examples of Embedded Systems
Embedded systems are all around you, usually without you noticing. In the home they control washing machines, dishwashers, microwaves and central-heating thermostats. In transport they run the engine-management and anti-lock braking systems in cars, and the controllers inside traffic lights. In healthcare they power devices such as pacemakers. In leisure and personal technology they appear in digital cameras, fitness trackers and MP3 players. In every case the same idea applies: a computer is built into the product to control one specific set of tasks.
Embedded vs General-Purpose Computers
A general-purpose computer, such as a desktop PC, laptop, tablet or smartphone, is designed to run many different programs. You can install new software, delete it, and use the same machine for writing, gaming, video calls and browsing. It has a full operating system, plenty of memory and storage, and is built to be upgraded over time.
An embedded system is the opposite. Its function is fixed when it is manufactured, its firmware is not meant to be changed by the user, and it usually has only the memory and processing power its single task requires. In short, a general-purpose computer is a flexible machine you adapt to many jobs, while an embedded system is a specialised machine dedicated to just one.