PROCESSORBacking Storage Main Memory Output Devices Input Devices Backing Storage

Backing Storage When the computer is switched off data has to be stored on a secondary storage device. Backing storage devices fall into two categories: Optical Magnetic Magnetic Devices Floppy Disc Hard Disc Zip Disc Magnetic Tape

Optical Device CD-ROM CD-Recordable CD-Rewritable DVD-ROM DVD-Recordable DVD-Rewritable

Sequential Access You want to play your favourite Spice Girl track ‘2 becomes 1’. This track is number 5 on the tape you would have to fast forward to this track. Which can take time. Random (Direct) Access You want to play your favourite West Life track ‘Flying without Wings’. You can send the player directly to any track and it will start playing the dong immediately. Sequential & Random (Direct) Access

Random (Direct) Access The system can go straight to the data it requires Sequential (Serial) Access Is a description of storage system where records must be searched in sequence, one after the other

Floppy Drive/Disk A floppy disk is small disk you can remove from a floppy Drive. Type of Access Direct/Random Speed of Access Slow because they need to rotate slower that hard drives Capacity 1.44 Mb Cost Very Cheap Function Storing small text files

USB Flash Drive Universal Serial Bus Taking over the floppy disk. Connects via the USB interface. Type of Access Direct/Random Speed of Access Medium Capacity 16 MG – 1GB Cost £10 - £200 Function Storing multimedia presentations, digital photos They are solid state devices, because they have no moving parts.

Hard Drive A hard disk is a disk with a magnetised surface. The surface is divided into tracks and sectors on which data is stored magnectecally. Cost 80Gb - £65 Function Storing Operating System Applications Files Type of access Random/direct Speed of Access Fast Capacity 80Gb – 250Gb

Zip Drive A high-capacity floppy disk drive. Zip disks are slightly larger than conventional floppy disks, and about twice as thick. Because they're relatively inexpensive and durable, they have become a popular media for backing up hard disks and for transporting large files. Cost USB - £49 In-built ££65 259Mb - £12 750Mb - £15 Function Storing large files Type of Access Direct/Random Speed of data Access Depends on the connection (USB) Capacity 250MB – 750MB USB drives are likely to make sip drives obsolete.

Magnetic Tape Varies in width and length. Commonly used for back-up. Capacity can vary from a few kilobytes to many gigabytes. Cost Basic tape is cheap 100Mb - £2500 Function Used for backup on a large mainframe system Type of access Sequenctial Speed of Access Slow Capacity 10Gb – 500Gb

CD ROM Optical disc capable of storing vast amounts of digital information. When a CD ROM is made, the data is moulded into tiny holes (PITS) on the clear plastic disc. Data is read by focusing a laser beam onto the tracks. When the laser strikes the area between the pits (LANDS) it is reflected and registers as a 1, and the light which hits a pit it registers as a 0 to give the binary information. PIT LAND LASER BEAM

Interface Part of a computer system that allows different devices to communicate with the processor by compensating for any differences in their operation.  Data transfer  Voltage conversion  Analogue to digital conversion