Section 12.3
Peripherals
12.3 Storage Devices
Most computer systems require a backing store for programs and data.
We are interested in:
- data integrity
- storage capacity
- access time
- data transfer rate
- low cost
12.3.1 Floppy Disks
The surface of the disk can be magnetised.
Formatting a disk marks out concentric tracks and sectors on both of the surfaces
of the disk.
12.3.2 Hard Disks
The hard disks inside PCs consist of one or more disk platters sealed inside a
casing.
They work in a similar but smaller way to disk packs.
The read/write heads float on a cushion of air about one millionth of an inch
off the surface of the disk.
CD-ROM
Advantages:
- Good storage capacity
- Modest transfer rate
- Fairly robust
Disadvantages:
- Only the manufacturer can store data
- Relatively large for the portable market
CD-R (WORM)
Allows data to be written once to the CD.
Advantages:
- Inexpensive method for data storage
- Can be read by CD-ROM drives
- Excellent for archiving
Disadvantages:
- Cannot be reused (although in some cases this may be an advantage)
- Capacity too small for entire HD backup
CD-RW
Can write data out several thousand times.
Advantages:
- Could be a replacement for a floppy disk
Disadvantages:
- Cannot be read by some older CD-ROM drives
DVD-ROM
Stores more using two layers on each side.
Advantages:
- Increased storage capacity
- Marginally faster data transfer than CD-ROM drives
Disadvantages:
- Cost of manufacture is higher (currently)
-
Recordable & Rewritable DVD Drives
There are currently many incompatible standards including
- DVD-R
- DVD-RW
- DVD-RAM (likely to become standard)
12.3.4 Magnetic Tape
Magnetic tape is used for:
- Backup
- Archiving
- Batch Processing
It is inexpensive, robust and has a large data storage capacity with a very fast
data transfer rate.
Mainframe Environment
A few systems still use tape reels.
Many use Terabyte Disk Farms.
Minicomputer Drives
There are a number of different formats available.
- QIC (Quarter Inch) Tape Streamers (35GB)
- DAT Tape Streamers (26GB)
- VHS Tape (4GB)
12.3.5 Non-volatile Memory
NVRAM is currently only used for storage in specialist embedded systems.
Uses:
- Black box flight recorders
- Satellites
- Fighter aircraft weapon systems
