Transcript Type of Access - Clydebank High School

Backing Storage
Input Devices
Backing Storage

PROCESSOR
Output Devices

Main Memory
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 & Random (Direct) Access
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.
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
Cost
Direct/Random
Very Cheap
Speed of Access
Function
Slow because they need
to rotate slower that hard
drives
Storing small text files
Capacity
1.44 Mb
USB Flash Drive Universal Serial Bus
Taking over the floppy disk. Connects via the USB
interface.
Type of Access
Cost
Direct/Random
£10 - £200
Speed of Access
Function
Medium
Storing multimedia
presentations, digital
photos
Capacity
16 MG – 1GB
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.
Type of access
Random/direct
Cost
80Gb - £65
Speed of Access
Fast
Function
•Storing Operating System
•Applications
•Files
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
Type of Access
USB - £49
Direct/Random
In-built ££65
259Mb - £12
Speed of data Access
750Mb - £15
Depends on the connection
(USB)
Function
Capacity
Storing large files
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.
Type of access
Sequenctial
Cost
Basic tape is cheap
100Mb - £2500
Speed of Access
Slow
Function
Used for backup on a large
mainframe system
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.
LAND
LASER BEAM
PIT
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