3.

Storage devices and media

Magnetic media and magnetic storage devices
Magnetic tape drives

A magnetic tape is a very thin strip of plastic which is coated in a magnetic layer. They are
read from or written to by a read/write head in a magnetic tape storage device. The data is
stored as a magnetized area (which represents a 1) or demagnetized area (which represents a
0) and is read from the tape using serial access.

Uses of magnetic tape

1. Use in applications where batch processing is used (for example, clearing bank cheques,
utility billing ).

2. Used as a backup media where vast amounts of data need to be stored.

3. Used in long-term archiving of data; magnetic tapes have huge data storage capacities
and are known to be very stable, which makes them ideal for long-term storage.

Advantages of magnetic tapes Disadvantages of magnetic tape

They are generally less expensive (per Very slow data access times because
byte) than the equivalent hard disk they use serial access,
drive.
The process of updating data using
It is a very robust technology and o not magnetic tapes using a master tape (the
deteriorate overtime original) and a transaction tape
(containing changes) to create a new
They have a huge data storage capacity.
master tape is a slow and can also
The data transfer rate is actually fast introduce errors

a strong magnet can corrupt data stored

on the tape.

Hard disk drives (HDD)

in a Hard disk drives (HDD) Data is stored in a digital format on the magnetic surfaces of the
hard disks (or platters).

3. Storage devices and media 1

 how HDD works:

1. voice coil Actuators are used to move the read/write heads

2. A read/write arm swings the read/write head back and forth across the platter(made from
glass, ceramic or aluminum and coated in iron oxide.); that is rotating at up to 10000 rpm
(revolutions per minute).

3. Each read/write head contains a tiny magnet which allows the data on the platter to be
read.

4. There are two read/write heads per platter (one for the top surface and one for the bottom
surface).

5. Data is stored in concentric, circular tracks; each track is broken up into sectors.

6. A map of the sectors is stored on the HDD and is known as a file allocation table (FAT);
when the computer wants to store new data, it looks at the FAT map to find out which
sectors are free and then moves the read/write heads to the correct location

Uses of fixed hard disk drives

1. To store the operating system, systems software and working data/files.

2. Storing applications software.

3. Used in real-time systems (for example control of a chemical plant) and in online
systems (for example, booking airline tickets).

4. Used in file servers for computer networks.

Advantages of fixed hard disk drives Disadvantages of fixed hard disk drives

They have a very fast data transfer rate They can be fairly easily damaged (for
and fast access times to data. example, if shut down incorrectly

They have very large memory They have many moving parts which
capacities. can affect their overall reliability.

Their read/write operation can be noisy

when compared to solid-state drives.

Portable hard disk drives

A portable hard disk drive (HDD) is an external storage device that is designed to be easily
portable and used with multiple computers or devices.

Uses of portable hard disk drives

3. Storage devices and media 2

 They can be used as backup systems to prevent loss of data.

They can be used to transfer data/files/software between computers.

Advantages of portable hard disk drives Disadvantages of portable hard disk

drives
The data access time and data transfer
rate are very fast. they can be easily damaged if the

They have a large memory capacity. Data transfer rate is not as fast as for
fixed hard drives.
They can be used as a method of
transferring information between
computers.

Optical media and optical storage devices

CD/DVD optical disks
CDs and DVDS are described as optical media built in to a computer or connected externally
via a USB cable and are read from or written to by optical storage devices
CDs and DVDs can be designated as: ‘R’ (write once only), ‘RW’ (can be written to or read
from many times) or ‘ROM’ (read-only).

CD-R and DVD-R

Uses

1. Home recordings of music (CD-R) and films (DVD-R).

2. Used to store data to be kept for later use or to be transferred to another computer.

Advantages of CD-R and DVD-R Disadvantages of CD-R and DVD-R

Cheaper medium than RW disks. Can only be recorded once; if an error

occurs then the disk has to be thrown
Once burned (and finalized) they
away.
behave like a ROM.
Not all CD/DVD players can read CD-
R/DVD-R.

CD-RW/DVD-RW
Uses

3. Storage devices and media 3

 1. Used to record television programmes which can be recorded over, time and time again
(although increasingly replaced by HDD recording systems).

2. Used in CCTV systems.

3. Can be used as a backup device for files and data.

Advantages of CD-RW/DVD-RW Disadvantages of CD-RW/DVD-RW

Can be written over many times. Can be relatively expensive media.

Can use different file formats each time Possible to accidentally overwrite data.
it is used.

Not as wasteful as R format because

the files/data can be added at a later
stage.

CD-ROM/DVD-ROM

Uses

1. These optical disks are read-only memory (ROM) which means they cannot be written
over and can only be read. They are a permanent method of data storage.

2. CD-ROM is used to store music files and to store software, computer games and
reference software (such as an encyclopaedia).

3. DVD-ROM has much larger storage and is used to store films; but now it is increasingly
used to store computer data and the evermore sophisticated games.

4. CD-ROMs and DVD-ROMs are used in applications where there is a real need to
prevent the deletion or overwriting of important data.

Advantages of CD-ROM/DVD-ROM Disadvantages of CD-ROM/DVD-ROM

They are less expensive than hard disk The data transfer rate/data access time
drive systems. is slower than for hard disks.

Blu-ray discs
Uses of Blu-ray discs

1. Home video consoles.

2. Storing and playing back movies

3. Storage devices and media 4

 3. data storage or backing up hard drives.

4. Camcorders can use this media (in cartridge form) to store movies.

Advantages of Blu-ray discs Disadvantages of Blu-ray discs

large storage capacity Relatively expensive discs.

fast data transfer rate. Encryption problems (which are used

to stop piracy) when used to store
The data access speed is also greater
video.
than with other optical media.
Introduction of HD (high definition)
Blu-ray discs automatically come with
DVD players has reduced the
a secure encryption system, which
advantages of using Blu-ray discs.
helps to prevent piracy

differences between DVD and Blu-ray are:

A blue laser , rather than a red laser is used to carry out Blu-ray read and write
operations.

Blu-ray can store up to five times more data than normal DVD because Using blue laser
light means that the pits and lands can be much smaller.

Single-layer Blu-ray discs use a 1.2 mm thick polycarbonate disk; however, dual-layer
Blu-ray and normal DVDs both use a sandwich of two 0.6 mm thick disks (i.e. 1.2 mm
thick).

Blu-ray disks automatically come with a secure encryption system which helps to
prevent piracy and copyright infringement.

The data transfer rate for a DVD is 10 Mbps and for a Blu-ray disc it is 36 Mbps (this
equates to 1.5 hours to store 25 GB of data).

Solid-state media and Solid-state storage devices

3. Storage devices and media 5

 Solid state technology has solved the latency issue in the HDDs. They do not rely on
magnetic properties and have no moving parts. The data is stored as 0’s and 1’s. They are
often referred as flash memories or flash drives.
Solid-state drives (SSD)

Uses:

1. Store files and applications

2. Storing operating systems

3. Can be used as a backup device

Advantages of SSD Disadvantages of SSD

More reliable and robust as it has no Less write operations per X day
moving parts (more thin) compared to HDDs

Lighter in weight in comparison with Still not used in all servers

HDDs

Low power consumption

Data access speed is way faster

compared to HDDs

Pen drives

Pen drives (memory sticks) are small portable devices that make use of solid-state technology
Uses of memory sticks/pen drives

1. Transporting files between computers or using as a backing store.

2. Used as a security device to prevent software piracy (known as a dongle).

Advantages of memory sticks/pen drives Disadvantages of memory sticks/pen

drives
Very compact and portable media.
Cannot write protect the data/files by
Very robust.
making it ‘read-only’.
Does not need additional software to
Easy to lose due to the small physical
work on most computers.
size.
They are not affected by magnetic
incorrect removal will corrupt the data
fields.
on the memory stick and make it
useless.

3. Storage devices and media 6

 Memory cards

memory card format:

» SD cards (secure digital card)
» XD cards (extreme digital card)
» CFast card (compact fast card).

Uses of memory cards

1. Storing photos on digital cameras.

2. Used as mobile phone memory cards.

3. Used in MP3 players to store music files.

4. Used as a backing store in hand-held computer devices.

Advantages of memory cards Disadvantages of memory cards

Very compact Have a lower storage capacity than

hard disks.
they are very durable.
Have a finite life regarding number of
They can hold large amounts of data.
times they can be read from or written
Digital devices are able to read and to.
write to memory cards, allowing the
they are more likely to be lost, stolen or
user to transport large collections of
damaged because they are small
data with them.
users will often be required to purchase
a card reader or USB converter to view
the data on a memory card.

3. Storage devices and media 7