1. Storage of Data Letts Chapter 6

2. Introduction Any system needs to store both programs and data and requires: n a main store for fast access storage; n at least one type of backing store for long term storage

3. Main Store n Main store: is in the CPU; can be accessed at very high speed without mechanical movement; is divided into locations each with a different address. n Main store usually contains two different types of memory: n Read Only Memory (ROM), which is permanent and its contents cannot be changed; n Random Access Memory (RAM) which is a temporary store used to store the current program and data and other items such as the screen contents.

4. Backing Store Backing store: n usually magnetic tape in a cartridge: n is usually accessed using read/write heads; n does not allow such fast access as main store; n stores its data until it is deleted n In direct access stores any data item can accessed without reading other data first. n In serial access stores all data before the required item has to be read first.

5. Direct Access Backing Stores The main types of direct access backing stores are: hard disks; floppy disks; CD-ROMs. n Each surface of a magnetic disk holds data in circular tracks. n Each track is divided into equal sections called sectors..

6. Hard Disks n Hard disks are usually fixed in the drive in a sealed unit n They are faster than floppy disks and store more data

7. Floppy Disks n Are easy to transport and exchangeable n Protected by a stiff plastic cover and data on the disk can be protected by a ‘write protect’ tab.

8. CD ROMS All types of compact disks can be read by a computer including music CD’s, photo CD’s and CD-ROMs n CD-ROMs are exchangeable and easy to transport n CD-ROMs store more data than floppy disks and are also faster n CD-ROMs are Read Only. The data is written during manufacture.