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Bits and bytes A computer only understands the numbers 0 or 1, or whether a switch is on or off. We call those 1’s and 0’s ‘bits’ – binary digits. A byte (made up of 8 bits) is enough computer memory to store a single character of data (e.g. the letter F). The computer uses a code to understand what each bit pattern means. Using the ASCII code, for instance, the letter F is 70 and has a bit pattern of 01000110.

ASCII for Capital Letters 65 A   78 N 66 B 79 O 67 C 80 P 68 D 81 Q 69 E 82 R 70 F 83 S 71 G 84 T 72 H 85 U 73 I 86 V 74 J 87 W 75 K 88 X 76 L 89 Y 77 M 90 Z American Standard Code for Information Interchange (ask-ee) is a code which represents English characters as numbers. Each letter is assigned a number. For example, A = 65. Most computers use ASCII codes. This makes it possible to transfer data from one computer to another by changing the ASCII code into a binary pattern.

ASCII for Capital Letters 65 A   78 N 66 B 79 O 67 C 80 P 68 D 81 Q 69 E 82 R 70 F 83 S 71 G 84 T 72 H 85 U 73 I 86 V 74 J 87 W 75 K 88 X 76 L 89 Y 77 M 90 Z

Decimal and binary When we write numbers in the decimal system, we write them in columns. Each column is 10 times bigger than the one before (right to left). Tens of millions millions 100000s 10000s 1000s 100s 10s 1s 1 So 1010 is 1000 plus 10 = 1010. Tens of millions millions 100000s 10000s 1000s 100s 10s 1s 1 11010 would be 10000 plus 1000 plus 10 = 11010.

In the binary system, everything is based on 2s, not 10s, so each column is twice as big as the one before. 128s 64s 32s 16s 8s 4s 2s 1s 1 So 1010 in binary is 8 plus 2 = 10. 128s 64s 32s 16s 8s 4s 2s 1s 1 11010 would be 16 plus 8 plus 2 = 26.

Binary patterns Using the binary system, convert the ASCII code into the binary pattern. The first row has been completed for you.

I take up more space than you. All computer data is stored in binary form. This does not only include text but images, sounds and movies as well. I take up more space than you. The more complex the data the more memory is used to store it.

The amount of data stored is measured in kilobytes (KB). Confusingly, 1KB is actually 1,024 bytes (210), not 1,000 as you might expect, but most people think in multiples of 1,000. 1 megabyte (MB) is 1,000 KB (220) 1 gigabyte (GB) is 1,000 MB (230) 1 terabyte (TB) is 1,000 GB (240).

Read Only Memory (ROM) When a computer is first switched on, it needs to load up the BIOS (Basic Input/Output System) and basic instructions for the hardware. These are stored in ROM (Read Only Memory). This type of memory is called non-volatile because it retains the data. Data stored in ROM remains there even when the computer is switched off. ROM can be found on the motherboard.

Random Access Memory (RAM) When a computer is started operating instructions, any computer programs that are opened and data are stored in the RAM (Random Access Memory) temporarily. The contents of RAM are constantly rewritten as the data is processed. When the computer is switched off all the data is cleared from the RAM. This type of memory is called volatile because it only stores the data while the computer is switched on. RAM sticks are found on the motherboard.

Storage devices and media There are two types of storage device: those that store data by magnetizing a special material that coats the surface of a disk, and others that store data using optical technology to etch the data onto a plastic-coated metal disk. Laser beams are then passed over the surface to read the data. The medium is what the data is actually stored on. Examples of media include floppy disks, CD-ROM and zip disks.

Storage capacity

Fixed storage

Removable storage With thanks to Evesham Technology.

Summary Data is stored using binary code (0 and 1). Computer memory is measured in kilobytes. Read Only Memory (ROM) is non-volatile because it cannot be changed. Random Access Memory (RAM) is volatile because it only works when the computer is switched on. There are two types of storage devices; those that use magnetic media and others that use optical media. Different types of media have different storage capacities. Storage devices can also be divided into those that are fixed and those that are removable.