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An abstraction of a computer

If we looked inside a mobile phone and tried to understand all of the different parts in it and how they worked together so we could make phone calls and text each other, we would very quickly be overwhelmed with complicated information. It's the same with any system. Imagine trying to understand how a car engine works by trying to make sense of each individual component, or trying to understand how a TV works by getting to grips with each part of a TV when we take the back off, or understanding how a plane flies. It's the same with any computer system. There are literally thousands of different parts and we can't possibly understand the engineering complexities of each one. For this reason, we need to simplify the system. We need to create a model of what we can see so that we can start taking our knowledge further without getting bogged down in too much detail.

A simplified model is also known by the fancy word  'abstraction'. We are taking a complex system and building an abstraction of it so we can push our knowledge further on without worrying about the details. When can build an abstraction of how computers work. Here it is:

This abstraction shows us a lot of information about very complicated computer systems:

• • input devices (e.g. a microphone, keyboard or mouse) capture data from the real world
  • they pass this data to the CPU
  • the CPU sends data to output devices (e.g. monitors or speakers)
  • the CPU sends data to RAM and also gets data and program instructions back from RAM
  • the RAM sends data to and from the CPU but also RAM sends data to and receives data from the storage devices (e.g. the hard drive)
  • the CPU doesn't deal directly with programs on storage devices. It deals directly only with data in RAM
  • if the CPU wants to store data or get back data from a storage device, all data must go via RAM.

Something that is actually very complicated is now something we can start to understand, all because we used an abstraction of what was real to make a simplified model, which we can understand. If you keep the above model in mind, you will find that it actually applies to nearly all computer systems you know, including mobile phones, tablet PCs, laptops and even things that might not seem like a computer system, such as a computer controlled microwave oven or washing machine, a burglar alarm or a firm alarm.

Q1. Tick whether each piece of hardware is an input device, an output device or a storage device. The first two have been done for you. If you are not sure about any of them then use the Internet or a text book to help you.

Q2. What does CPU stand for?
Q3. Why do computers need storage devices?
Q4. Sometimes, computers start to behave strangely, in a way that is not supposed to happen. One piece of advice when this happens is to turn the computer off then on again. Explain why this advice is given.
Q5. Why might two identical computers work at different speeds, if one computer had twice as much RAM as the other?
Q6. When you read about RAM and storage devices, you might see the terms 'volatile' and 'non-volatile' memory. What do they mean?
Q7. Look up 'cache' on the Internet (pronounced 'cash'). What is cache?
Q8. What is meant by booting-up a computer?
Q9. Computers come with ROM. There is a special program inside ROM that runs when you boot your computer up. Using the Internet, find out what jobs this special program carries out.
Q10. Do some research. Find out what dual-core, quad core and multi-core processors are and why they are important.

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