1. Backing Storage

2. Learning Intentions To Understand: Different types of Backing Storage
Their relative advantages / Disadvantages
Their relative capacities

3. Backing Storage
Backing Storage Devices are hardware which is used to store programs and data permanently onto Backing Storage Media.
Computers need backing storage because data in Main Memory is lost when the computer is switched off.

4. Backing Storage Device Media Tape Drive Floppy disk drive
Hard Disk drive
CD-ROM drive
DVD-ROM drive
CD Rewriter drive
DVD Rewriter drive
USB Flash drive
Media
Magnetic tape
Floppy disk
Hard Disk
CD-ROM
DVD-ROM
CD-Recordable
CD-Rewritable
DVD-Recordable
DVD-Rewritable
Flash ROM

5. Magnetic Tape Still used to hold high quality audio.
Now widely used as a backup system for computer data.
Capacity depends on the length
of tape but usually between
10Gb and 100Gb.
Data is often compressed.

6. Floppy Disk Plastic coated with a magnetic material.
Easily damaged by heat, magnetism etc – data should be backed up.
Can be write protected - stops accidental over-writing.
Capacity id 1.44Mb.

7. Hard Disk Hard disks covered in magnetic material.
Several disks in a platter.
Rotate very fast.
Read/Write heads copy data to disk and read from it.

8. Hard Disks If heads collide with the disk, this is called crashing.
This could cause all data to be lost.
Hold 40Gb – 1Tb

9. CD ROM Read Only – can’t be written to. Music CDs
Surface of the disk has Pits and Lands.
A laser shines on these and the reflected light is interpreted as 1 or 0.
Can hold 650 – 700Mb

10. DVD-ROM Read only – can’t be written to. Same technology as CD.
Capacity: 4.7 – 17 Gb.
Tracks of Pits & Lands closer together – smaller pits & lands.

11. CD – Recordable (CD-R)
Data is written to the disk using a high powered laser.
This high powered laser creates the Pits & Lands.
A lower powered laser is used for playback.
Can only be written to once.
Same capacity as a CD-ROM, 650 – 700Mb

12. CD – Rewritable (CD RW)
Can be recorded onto, erased and re-written to.
Uses different powered lasers to Write data, Erase data and Read data.
Can be re-written a few thousand times.
Capacity is 650 – 700Mb.

13. DVD-R DVD-RW DVD-R DVD-RW 4.7Gb capacity Similar to CD-R
Recorded to once.
Different powered lasers to record and playback.
DVD-RW
4.7 – 9.4Gb capacity.
Similar to CD-RW
Can be re-written to thousands of times.
Different powered lasers to record, erase and playback data.

14. USB Flash Drives Stands for Universal Serial Bus.
They are solid state devices – they have no moving parts.
They use Flash ROM which can be recorded to thousands of times.
Capacity between 2Gb – 128Gb.

15. Pupil Task Use the Internet to complete the table on the next slide.
You can use a Word document in necessary.

16. Comparison Media Speed Cost Capacity Tape Floppy Disk Hard disk CD-ROM
DVD-ROM
CD-R
CD-RW
DVD-R
DVD-RW
Flash ROM