Know what a computer is used for Understand the difference between hardware and software Be able to describe the way that data is stored in a computer system Computer systems are commonplace now in every part of our lives. But what, exactly, is a computer system? Computers come in a huge variety of shapes, and sizes. You will be most familiar with Personal Computers (PCs) the small computer on your desk, or the laptop in your bag. However there are some computers that fill whole buildings and others that are small enough to fit in a slim mobile telephone. Whatever the size, all computers do the same thing a device that stores and processes information according to a set of instructions. In other words, a computer is a device that you feed data into and it does something with the information (processes it) based on some instructions (a program) that it has been given. A computer is, basically, a data processing system. The huge room-sized 'mainframe' above and the tiny mobile phone circuitboard below it are both computers Data (eg mouse clicks) goes IN Information (word documents etc) comes OUT It doesnt matter what type of computer we are looking at, or what programs the computer is running, it always takes in data and does something with it in order to produce information. A spreadsheet running on a personal computer: Or a game being played on a games console (these are computers too)... A computer system is made up of hardware and software. Hardware is a general term for all the physical components that you can see and touch: the keyboard, the mouse, the monitor, the CPU..... Software refers to the programs that control the hardware. There are two types of software: Systems Software - this is software that allows the hardware to run properly, and includes Windows, MacOS, Linux etc Applications Software - this refers to programs that allow the user to do specific tasks: word processing, spreadsheets, multimedia presentations etc. Everything that is stored and processed inside a computer (all data, information, instructions, files, images, etc.) is stored as numbers. This is because computer only understands numbers, nothing else. Numbers are made up of digits, so we could say that computers only understand digits. Because of this, we say that computers are digital devices. how do you store text and pictures as numbers?! The solution is to use numeric codes: Different letters in a text document are given different numeric codes Different pixels (coloured dots) in an image are given different numeric codes Different sounds in a music file are given different numeric codes Everything is numbers. Everything inside a computer is actually a Binary number (see the explanation on the next slide). If you took a peek inside the memory of a computer you might see the following Binary numbers: These numbers could be the codes for some text, or they could be the codes for some pixels in an image, or they could just be numbers! A computer only understands a particular type of number called Binary. This rather strange number system (and you really don't need to learn this!) only uses the digits 0 and 1. So a typical binary number might be The reason for the use of binary numbers is that the electronic devices in a computer (the CPU, the RAM, etc.) have parts that can only be turned on or off. We can use binary numbers to control these ons and offs: off = 0, on = 1 What is a Bit? A bit is a Binary Digit (the word comes from Binary DigIT) Because it is a binary digit, a bit can only have the value 0 or 1. (This is different from our normal decimal digits which can have any value between 0 and 9.) This binary number is four bits long: 1101 What is a Byte? Bits are usually grouped into groups of 8, and each group is called a Byte. Here is are a bunch of bytes (all exactly 8 bits long): Bytes are the standard unit of storage for all computing devices: Hard drive size is measured in bytes, file size is measured in bytes, RAM size is measured in bytes. So, next time someone tells you that they have a 500 GB hard drive, you will know that it can store 500 billion bytes of data A thousand bytes is known as a kilobyte (kB) 1,024B = 1kB A million bytes is known as a megabyte (MB) 1,000,000B = 1MB A thousand million bytes is called a gigabyte (GB) 1,000,000,000B = 1GB A million million bytes is called a terabyte (TB) 1,000,000,000,000B = 1TB Read & make notes from the link on the wiki.