HNC COMPUTING - COMPUTER PLATFORMS 1 Computer Platforms Week 2 Backing Storage

HNC COMPUTING - COMPUTER PLATFORMS 2 Aims Understand how data is stored Be able to use the binary system to represent ASCII characters Discuss the different types of backing store and understanding the meaning of CD, CD-R etc

HNC COMPUTING - COMPUTER PLATFORMS 3 How is data stored? Bits and bytes – –A computer only understands the numbers 0 or 1,true or false, or whether a switch is on or off. – –We call those 1s and 0s ‘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). – –Half a byte is known as a nibble (made up of 4 bits) – –Using the ASCII code, for instance, the letter F is 70 and has a bit pattern of

HNC COMPUTING - COMPUTER PLATFORMS 4 How is data stored? Cont. ASCII for Capital Letters 65A 78N 66B 79O 67C 80P 68D 81Q 69E 82R 70F 83S 71G 84T 72H 85U 73I 86V 74J 87W 75K 88X 76L 89Y 77M 90Z 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.

HNC COMPUTING - COMPUTER PLATFORMS 5 How is data stored? Cont. Decimal When we write numbers in the decimal system, we write them in columns. Each column is ten times bigger than the one before (right to left). Tens of millions millions100000s10000s1000s100s10s1s 1010 So 1010 is 1000 plus 10 = Tens of millions millions100000s10000s1000s100s10s1s would be plus 1000 plus 10 =

HNC COMPUTING - COMPUTER PLATFORMS 6 How is data stored? Cont. In the binary system, everything is based on 2s, not 10s, so each column is twice as big as the one before. 128s64s32s16s8s4s2s1s 1010 So 1010 in binary is 8 plus 2 = s64s32s16s8s4s2s1s would be 16 plus 8 plus 2 = 26.

HNC COMPUTING - COMPUTER PLATFORMS 7 You have ago

HNC COMPUTING - COMPUTER PLATFORMS 8 How is data stored? Cont. All computer data is stored in binary form. This not only includes text, but images, sounds and movies as well. The more complex the data, the more memory is used to store it. This does not take up as much memory… …as this.

HNC COMPUTING - COMPUTER PLATFORMS 9 Data Storage 1 megabyte (MB) is 1,000 KB (2 20 ) 1 gigabyte (GB) is 1,000 MB (2 30 ) 1 terabyte (TB) is 1,000 GB (2 40 ). Confusingly, 1KB is actually 1,024 bytes (2 10 ), not 1,000 as you might expect, which is same for 1MB (1,024 KB), 1GB (1,024 MB) and 1TB (1,024 GB), but most people think in multiples of 1,000.

HNC COMPUTING - COMPUTER PLATFORMS 10 Types of backing storage Computers need backing storage outside the CPU to store data and programs not currently in use. There are three main types of storage device: – –Those that store data by magnetizing a special material that coats the surface of a disk. – –Those 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. – –Flash drives use solid state technology and store data in a similar way to the BIOS chip.

HNC COMPUTING - COMPUTER PLATFORMS 11 Backing storage The hard disk of the computer stores the system information, programs and data that the computer uses every day. ) Computer servers will use RAID (Redundant Array of Inexpensive Disks ) systems with many hard drives to provide huge capacity and safer storage. The drives can be mirrored so that data written to one of them is also written to others, so if one drive fails, the others just take over.

HNC COMPUTING - COMPUTER PLATFORMS 12 Backing storage Removable hard drives plug into the USB port and can be used for backup or transfer of data to another computer.

HNC COMPUTING - COMPUTER PLATFORMS 13 Backing Storage There are two main types of optical storage: CD and DVD. They look exactly the same, but DVDs hold much more data than CDs and need different drives to read them. CD-ROMs are read only – you can read data from them but can’t write more data to them. CD-Rs allow you to write data once, but you can’t write over it. CD-RWs allow you to write data and then record new data over it. DVD-Rs and RWs follow the same pattern. You need special software to write to CDs and DVDs – you cannot simply copy files to them.

HNC COMPUTING - COMPUTER PLATFORMS 14 Conclusion We discussed how data is stored How to use the binary system to represent ASCII characters Discussed the different types of backing store and understanding the meaning of CD, CD-R etc