Embedded systems

Your washing machine has a computer inside it, and that computer will never run a game, a web browser, or anything else you install. It was built for one job and it will only ever do that job. Could you say, in a single line, exactly what that job is? It is a few easy steps to get there. The first is saying what one of these computers even is. The one in a washing machine, the one in a set of traffic lights, the one in a pacemaker.

Last of the six in Inside the computer, and the only one you can point at in your own kitchen. Nothing here leans on the last four videos, only on Hardware and software.

So here is the name, and the one sentence that carries it. An embedded system is a computer built into a larger device, dedicated to controlling one function of it. The test is not size: a phone is a very small computer and is not one, while a car's braking controller is. Two questions decide it, and they are worth asking out loud. A laptop, and a washing machine. Which one is the embedded system, and how do you know? The washing machine. It is inside something larger and will never be given another job; the laptop is the whole device and runs whatever you install on it. And that sentence is one a lot of students already have. An examiner's report says many students showed an understanding of the idea that an embedded system is a small system contained within another system. The two tests, then, in plain words. It is built inside something bigger than itself, and it will only ever do the one job. Traffic lights and a pacemaker pass the same two questions. A laptop, a desktop and a phone fail both, because each one is the whole device and will run anything you put on it.

Now the characteristics, because one specification asks for three of them and the third is the one that runs out. It has a single dedicated purpose. It is built inside a larger system rather than being the device itself. Its hardware is dedicated, and its sensors feed only that system. It is small, cheap and draws very little power. And its program is held permanently in the chip as firmware, which means software built in rather than installed by anyone. One warning about repeats before you write three of those down. Three answers often come back that look different from each other and are not. It does one job. It has a single purpose. It is dedicated to one task. How many characteristics is that, and what has gone wrong? One. All three say the same thing in different words, and a marker reads them as a single point. An examiner's report says where the third one comes from: fewer candidates were able to provide a third point. Those that did most commonly identified the dedicated hardware or gave an example such as the sensors are only providing data for this system. So take your three from different rows. The purpose, then where it sits, then the hardware or the sensors.

Now back to that one job from the start, because it is the question these things actually get asked. Not what an embedded system is, but what that particular one is doing. A washing machine contains an embedded system. State the purpose of this embedded system. And the answer that comes back is that it has one specific purpose. An examiner's report on that question: over three-quarters of the candidates did not gain the mark for this question. Many candidates restated the question, by saying an embedded system has one specific purpose. Every word of that answer was already in the question. So what is it missing? The job itself, which is the part that answer never gives. What it is measuring or controlling, and what it is working towards. The same report prints the answer that scores: to monitor the water temperature until it reached the required temperature. There are three pieces in that. A verb, monitor. A thing measured, the water temperature. And a condition it is working towards, the temperature the wash needs. Can you build those same three pieces for a set of traffic lights? One answer that scores: to switch the lights in a set order on a timer, until a sensor detects a car waiting at the side road. Here is the question you put to the paper every time. What is it actually doing. Not what an embedded system is, but what that one, in that device, is doing.

One more habit, and it costs nothing to build. It is about where you look before you answer. A question describes a car, then asks you to name two embedded systems in it and state what each one does. Two of the answers that come back are a washing machine and a microwave. Both are perfectly correct about embedded systems, and both are worth nothing. Why does a correct answer about a washing machine earn nothing here? Because the question was about the car. Nothing was misunderstood; it is an answer to a question nobody asked. An examiner's report puts it plainly: some candidates provided examples of embedded systems such as a washing machine, a microwave and a fridge-freezer. This was not appropriate to the context of the question. The answers that did score stayed inside the car. Satellite navigation, automated lights, automated wipers and parking sensors, each one with the job it does. And one more line from a report: some candidates repeated that it was built into the car but this was provided in the question. So underline the object in the question before you write a word, and cross out anything you were simply told. Nothing in the question is an answer to the question.

Four things to walk out of here with. Questions first, answers after. How would you define an embedded system, in one sentence? An embedded system is a computer built into a larger device, dedicated to controlling one function of it. Now three characteristics: which three, with no two of them the same idea? One job and one only. It sits inside a bigger machine. And the hardware and sensors belong to it alone. Try an unseen one. A central heating thermostat: what is its embedded system doing? Something like this. The thermostat's system monitors the room temperature and keeps the boiler on until the room reaches the setting it was given. One more. Why would a microwave earn nothing in a question about a car? Because it is not in the car. The answer has to be about the device the question put in front of you. And the washing machine from the start comes out in one line. Its purpose is to monitor the water temperature until it reaches the temperature the wash needs.

The thumbs up marks the ones you could answer cold, and whatever is left without one is where to spend your next twenty minutes. Come back to those in a few days and they settle.

That completes Inside the computer: the parts, the loop they run, the numbers that make it quick, and the computers hiding inside everything else.

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