1. Backing Storage
Chapter 18

2. Backing Storage Devices
Backing storage devices allow us to store programs and data so that we can use them later
Floppy Disk drive
Tape drive
CD-ROM drive
Hard Disk drive
CD-R, CD-RW drives
DVD, DVD-R drives
USB Flash drive

3. Backing Storage Media Device Media
Backing Storage Media is the material used in each device
MEDIA DEVICE
Floppy Disk Floppy Disk Drive
Hard Disk Hard Disk Drive
CD-ROM CD-ROM Drive
Magnetic Tape Tape Drive
USB Flash Stick Flash ROM Drive
Media
Device

4. Floppy Disk A floppy disk is made out
of flexible plastic and is coated
with magnetic material.
The plastic disk is inside
a protective case.
Floppy disks are very easily damaged
They have a very small capacity (1.44Mb)

5. Hard Disk Solid disk (made of metal or very hard plastic)
Permanently fixed inside the computer (or close by it in its own box)
A hard disk is not portable like a floppy disk.
READ/WRITE HEADS
DISK

6. Magnetic Tape Stores lots of data as they have a large capacity
Reading from and writing to magnetic tape is much slower than using a magnetic disk.
Cheaper than storing data on magnetic disk.

7. CD ROM High capacity storage medium
Data is stored on surface of the CD in a series of pits
Pits are read by shining laser light onto the surface of the disk.
CD rotates at a very high speed and laser beam is reflected off the disks surface.
Data cannot be written to CD ROM once it has been produced

8. CD-R (Recordable)
Data is written onto the disk using a special disk drive unit.
The unit burns a permanent pattern into the surface of the disk using a high precision laser beam.
CD-R disks can only be written to until the disk is full

9. CD-RW (Rewriteable)
Data is written and rewritten onto the disk using a special disk drive unit.
The unit uses a high powered laser beam with 3 states
High – used to record data
Medium – used to erase data
Low – used to read the data
CD-RW (CD-Rewritable) disks can be written and rewritten many times

10. DVD ROM Stores greater amounts of information (4.7 – 17 gigabytes)
A DVD can store more information because:
Pits are smaller
Can have two layers on each side and be double sided
DVD-ROM cannot be written to once it has been produced

11. DVD-R & DVD -RW DVD-R (Recordable) DVD-RW (Rewritable)
Write once medium
Disk can only be written to until the disk is full
DVD-RW (Rewritable)
Disks can be written and rewritten many times

12. USB Flash Drive USB – Universal Serial Bus
Device used to store data, such as picture and movie files
USB Flash Drive is a Solid State Device as there are no moving parts
Storage capacities of between 16Mb to 2Gb

13. Types of Access Random (Direct) Access Sequential Access
Ability to locate data straight away, wherever it is stored and open it up
Fast access to files
Sequential Access
Retrieving data in the order that it was stored
Slower access to files

14. Access Devices Random (Direct) Access Sequential Access
Floppy Disk Drive
Hard Disk Drive
CD-ROM Drive
Sequential Access
Tape Drive

15. Storage requirements for Different Applications
Different Applications have different storage requirements
Space taken up by the Application
More or Less fixed when installed
Also depends on Installation option
Basic
Full
Custom
Size of application may grow with
Updates
new versions
extra features – plug-ins

16. Storage requirements for Different Applications Continued
Space taken up by any files produced using the application
Depends on type of Application
Multimedia Files require large storage space
Music
Video
High Quality Graphics
One hour of digital video = 13 Gb
One way to save space is Compression