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Computer Basics
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In order to write software, it helps to know a little about the fundamentals of how a computer works. Here we give a quick explanation of the important things you need to know. You may want to skip this section if you are already familiar with these topics.

Every computer, tablet and smart phone at a basic level, works in pretty much the same way. Here's a brief description of some of the main components.

CPU

The Central Processing Unit or CPU is the 'brain' of the computer, it takes a list of instructions (a software program) from the memory and executes them. It can perform mathematical and logical calculations and decide what to do depending on the results. It can also move data around and get input and output from the things it is connected to.

ROM

ROM or Read Only Memory can store data or programs represented as a list of numbers. The data does not change, even when the power is removed.

RAM

RAM or Random Access Memory can also store data or programs but the information can be modified and is lost when the power is removed.

Hard Drive

A hard drive is kind of inbetween ROM and RAM. It can store data like RAM, that can be modified by the CPU but the data is still kept when the power is removed. The drawback with hard drives is that they work much more slowly than RAM and ROM, this is why many computers use hard drives for keeping programs and data that are then copied (or loaded) into RAM when they are required. Also, the price of hard drives in terms of how much data they can store is much cheaper than RAM or ROM.

Flash

More often nowadays and especially in tablets and mobile phones, instead of a hard drive a type of memory called 'flash' is used. This kind of memory is used in a similar fashion to a hard drive but has no moving parts. It can be physically much smaller than a hard drive and is therefore good for mobile phones although the technology is now used in PCs in SSD or Solid State Drives which can be a direct replacement for a hard drive. The data in this memory can be modified but it is still there when the power is removed. This type of memory can also be found in memory cards that can be used to boost the amount of data that can be stored on your phone, tablet or camera, such as SD Cards. It is faster than a hard drive but not as fast as ROM or RAM.

Input Output Devices

A computer can only communicate with the outside world through input and output devices. The main input and output devices that a computer has are the keyboard, mouse and screen but literally thousands of devices can be attached to a computer.

At a lower level the CPU uses 'ports' that are physically connected to other devices and can send and receive data. Nowadays it is not very often that a software developer needs to directly access these ports as the operating system and drivers handle them.

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