Pages in this set

Page 1

Preview of page 1
Storage Devices

Page 2

Preview of page 2
Primary & Secondary Storage
Primary Storage
­ Volatile storage, such as RAM, is primary storage
­ All contents lost when machine switched off
­ Good practice to make regular back-ups
Secondary Storage
­ Non-volatile, more permanent storage for
software and data files
­ For example:
· Magnetic Tape, Magnetic Disks,…

Page 3

Preview of page 3
File Processing
Method usually depends upon whether every record
needs to be processed.
Sequential Processing
­ Every record has to be read. Typically used in a payroll
situation.
Random Processing
­ Each record has its own address allowing direct access
· Address can be calculated from a unique key
·…

Page 4

Preview of page 4
Floppy Disks & Zip Disks
­ 3.5" Floppy Disk
· Thin plastic disk (mylar) covered in metal oxide in a hard
plastic case.
· HD (high-density) disk can store 1.44 Mb
­ Zip Disk
· Slightly larger than floppy but similar construction
· Hold 100Mb or 250Mb of data
­…

Page 5

Preview of page 5
Hard Disks
PC
­ One or more platters in a sealed casing.
­ Typically 5Gb to 30Gb as of Spring 2001.
Minis & mainframes
­ May be fixed or removable
­ Fixed are faster, more reliable, greater storage capacity
­ Similar storage in concentric track, but on multiple platters,
giving…

Page 6

Preview of page 6
Hard Disk layout

Page 7

Preview of page 7
Magnetic Tape
Magnetic Tape is obviously a serial medium.
­ Have to read through tape to find a required record
­ Updates require creation of a new tape
· Data cannot be changed in situ
Cheap and convenient for backup
­ Cartridge tape for PCs can store up to 20Gb

Page 8

Preview of page 8
Magnetic Tape
101
111
011
000
110
110
001
001




Data record in frames across the tape
One frame represents one byte
Frames form tracks along the tape, typically 9
tracks ­ 8 data tracks and one parity track

Page 9

Preview of page 9
Other Devices
CD-ROM
­ Stores up to 700Mb.
­ Various data types
­ Read-only. Read by reflecting a laser beam off the surface
and detecting the presence or absence of tiny pits which will
have been burned into the surface to represent binary digits
CD-R
­ Similar to CD-ROM, but…

Page 10

Preview of page 10
Other Devices
Magneto-Optical Disks
­ Integrate optical and laser technology for read and write storage.
­ A 5.5" disk can store up to 2.6 Gb.
­ Still under development, but may replace magnetic disks when price
and speed permit.
Microfiche
­ COM (computer output on microfilm) devices create the4" by…

Comments

No comments have yet been made

Similar ICT resources:

See all ICT resources »