This document discusses different types of backing storage used to permanently store programs and data, as main memory is erased when a computer is turned off. It describes hard disks, CDs, DVDs, solid state drives, USB flash drives and their typical storage capacities. It also identifies whether each type of backing storage media provides sequential or random access to stored data.

1. Backing Storage

2. Backing Storage
 Computers need backing storage because data in main memory is lost when
the computer is switched off.
 Backing storage is used to store programs and data permanently.

3. Backing Storage
 Hard Disk
 Magnetic disk
 Typical storage: 500Gb – several Tb

4. Backing Storage
 CD-ROM
 Optical disk, uses laser to read
 Typical storage: 650Mb

5. Backing Storage
 DVD
 Optical disk, uses laser to read
 Typical storage: 4.7Gb

6. Backing Storage
 Solid State Drive
 Data stored on microchips, faster (and more expensive) than Hard Disk Drive
 Typical storage: Up to 1Tb

7. Backing Storage
 USB Flash Drive
 Data stored on microchips but not as fast or reliable as SSD
 Typical storage: Up to 1 Tb

8. Backing Storage
Backing Storage Media Sequential or
Random
Magnetic Tape Is mostly used for backing up data, all storage
locations are one after the other.
Sequential
Hard Disk Random
CD-ROM Random
DVD-ROM Random
CD Random
CD-RW Rewriteable CD allows the user to record over
data or delete individual files.
Random
DVD-R Random
DVD-RW Random
USB Random

9. Backing Storage
 Sequential vs Random Access
Sequential
Random