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.
Cost80Gb - £65
Function•Storing Operating System•Applications•Files
Type of accessRandom/direct
Speed of AccessFast
Capacity80Gb – 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.
CostUSB - £49In-built ££65259Mb - £12750Mb - £15
Function
Storing large files
Type of AccessDirect/Random
Speed of data AccessDepends on the connection (USB)Capacity250MB – 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.
CostBasic tape is cheap100Mb - £2500
FunctionUsed for backup on a large mainframe system
Type of accessSequenctial
Speed of AccessSlow
Capacity10Gb – 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
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