Fixed hard disks are used for storing operating systems and applications on a computer. They have high access speeds and storage capacities but cannot be removed from the computer. Portable hard disks can store large files and transfer them between computers, but can be easily stolen. Magnetic tapes provide extremely large storage capacities for backups but have slow access speeds. Optical disks like CDs and DVDs are used to distribute software, movies and files but have slower data rates than hard disks. Solid state storage like memory sticks are small, robust and portable but have lower capacity and speeds than hard disks. Backups protect against data loss by making copies of files and storing them separately from the originals.

1. STORAGE DEVICES
AND MEDIA
IGCSE CHAPTER 3
Anjan Mahanta
anjan.mahanta@satreephuketipc.com

2. Backing storage devices and media
● Data needs a material on which to be stored (called the storage media) and the
device recording the data onto the storage media is called the storage device.
● Backing storage is used for the storage of programs and data that are not
needed immediately by the computer.
● They are also used for storing backups of programs and data in case the
originals are damaged or destroyed.
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3. Magnetic Backing Storage Media
Magnetic backing storage media are those types of media including
magnetic disk and magnetic tape where data is stored by writing a
magnetic pattern onto the magnetisable surface of the media.
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4. Fixed Hard disks and drives
● Fixed hard disks consist of a series of disks coated with a
magnetic material and a series of read/write heads which record
data onto the surface or read it off the surface.
● Fixed hard disks are used to store operating systems,
applications software (i.e. the software you use to complete
tasks such as word-processing software), and any files of data
needed by the user.
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5. Fixed Hard disks and drives
● Fixed hard disks are, as the name suggests, fixed in the computer and are not designed to
be portable.
● Fixed hard disks in PCs and laptops are used for storing files that have been created using
software and then saved, e.g. C:/My Documents/letter.doc
● Fixed hard disks are used for online processes.
● Many fixed hard disks are used in file servers for networks.
● Because many users will want access to this store, the speed at which data is accessed and
transferred needs to be very high.
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6. Fixed Hard disks and drives
Advantages of fixed hard disks:
● A very high access speed (the speed of finding and reading data off
the disk).
● A very high transfer rate (the speed of storing data onto the disk).
● A very high storage capacity
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7. Fixed Hard disks and drives
Disadvantages of fixed hard disks:
● Fixed hard disks cannot be transferred between computers, unlike
a portable hard disk.
● The hard disk cannot be taken out of the computer and locked
away for security purposes.
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8. Portable Hard disks and drives
● Portable hard disks are also used to store very large files which
need to be transported from one computer to another.
● Generally portable hard disks are more expensive than other
forms of removable media but their very large storage capacity,
high access speed, and transfer rate are the reasons why they are
chosen.
● Portable hard disks are used for reasons other than the back-up of
data and programs, e.g. by a writer who works in two or three
locations during the week.
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9. Portable Hard disks and drives
Advantages of portable hard drives include:
● Their very large storage capacity means large files can be
transferred between computers.
● They are very fast at accessing and storing files so transferring
large files such as multimedia files takes little time.
● They can be attached to and used by any computer that has a USB
port.
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10. Portable Hard disks and drives
Disadvantages of portable hard drives include:
● Their size and portability means they are easily stolen.
● lt makes it easy for employees to copy confidential data such as a
medical database which is a security risk to companies /
organisations.
● Their use with lots of different computers can mean there is a
danger of viruses being transferred.
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11. Magnetic tapes
Magnetic tape stores data on a plastic tape coated with a magnetic layer.
Here are the main features of magnetic tape:
● Magnetic tape has a huge storage capacity.
● Magnetic tape is used to back up the data stored on hard disks.
● Because it takes time to move the tape to the position where the data
is stored, tape storage is much less common than disk storage.
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12. Magnetic tapes
● Magnetic tape is used in any application where extremely large storage
capacity is needed and the speed of access is not important.
● Magnetic tape provides serial access.
● Magnetic tape is also used in a variety of batch processing applications
where the computer can just be left to process the data without any
human intervention during the processing.
● Examples of this include reading bank cheques, payroll processing and
general stock control.
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13. Magnetic tapes
Advantages of magnetic tape include:
● They have extremely large storage capacities and this makes them
ideal for backup purposes where all data and programs need to be
stored.
● They are less expensive compared to similar capacity magnetic hard
disk drives.
● The data transfer rate is high (writing to tape).
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14. Magnetic tapes
Disadvantages of magnetic tape include:
● They are not suitable for an application that requires fast access to
data because the access speed is low.
● In order to update details on a tape it is necessary to create a new tape
containing some of the previous details along with the updated details.
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15. Optical Drives
● Optical drives are storage devices that make use of lasers to read
data off optical disks.
● Optical disks are flat circular disks on which data is stored as a
series of bumps.The way the bumps reflect laser beam light is used
to read the data off the disk.
● CDs are used to hold large files (<1 gigabyte) and are ideal for
holding music and animation files. DVDs have a much larger
capacity (4.7 to 8.5 gigabytes) and are used mainly for storing
films/video.
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16. CD ROM
With CD ROM:
● Data is read only
● Data is stored as an optical pattern
● There is a large storage capacity (700 Mb). They can be used for the distribution of software.
Advantage:
Once written, data cannot be erased, making it useful for the distribution of software/ music or
backing up.
Disadvantage:
Data transfer rate and access rate are lower than for a hard disk.
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17. DVD ROM
DVD ROM (digital versatile disk read only memory)
DVD ROM is used for the distribution of movies where you can only read the data off the
disk. A DVD ROM drive can also be used for reading data off a CD. DVD is mainly used for
the distribution of films, computer games and multimedia encyclopedias.
Advantage:
High storage capacity means full-length movies can be stored.
Disadvantages:
● The user cannot store their files on the disk.
● Older computers may not have a drive capable of reading DVDs.
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18. CD R (CD recordable )/ DVD R (DVD recordable)
● CD R allows data to be stored on a CD, but only once. DVD R allows data to be
stored on a DVD once. Both these disks are ideal where there is a single 'burning' of
data onto the disk. For example, music downloaded off the internet could be
recorded onto a CD in case the original files were damaged or lost.
● They can be used for archive versions of data. Storing archive data on the fixed hard
disk would clutter up the disk so it is better to store it on removable media and keep
it in a safe place. DVD R is ideal for storing TV programmes where you do not want
to record over them.
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19. CD RW (CD re writeable)
A CD RW disk allows data to be stored on the disk over and over again - just
like a hard disk. This is useful if the data stored on the disk needs to be updated.
You can treat a CD RW like a hard drive but the transfer rate is less and the
time taken to locate a file is greater.The media is not as robust as a hard drive.
Advantages:
● Re-writable, so they can be re-used. The data stored can be altered.
Disadvantages:
● The data transfer rate is lower than for a magnetic hard disk.
● Optical drives such as CD RWare more easily damaged than hard drives.
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20. DVD RW
DVD RW (digital versatile disk read/ write)
A DVD RW drive can be used to write to as well as read data from a DVD. DVD
RW are sometimes called DVD burners because they are able to be written to and
not just read from.
Like CD RW, they are ideal for storing data that needs regularly updating.
Typical storage capacities are:
● 4.7Gb for older DVD drives
● 8.5 Gb for latest DVD drives
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21. DVD RAM
DVD RAM has the same properties as DVD RW in that you can record data onto it many times
but it is faster and it is easier to overwrite the data. A typical storage capacity for DVD RAM is
10 Gb. DVD RAM is used for the storage ofT V/film at the same time as watching another
program.
Advantages
● Can read and write at the same time
● Fast transfer rate
● Fast access rate
Disadvantages
The devices are expensive compared to other devices
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22. Blu-ray
● The Blu-ray disk is an optical disk that has a much higher storage
capacity than a DVD. Blu-ray disks have capacities of 25Gb, 50Gb,
and 100Gb.
● These high capacity Blu-ray disks are used to store high definition
video.
● They are used for storing films; a25Gb Blu-ray disk is able to store
2 hours of HDTV or 13 hours of standard definition TV.
● lt is possible to play back video on a Blu-ray disk while
simultaneously recording HO video.
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23. Solid State Backing Storage
● Solid state backing storage is the smallest form of memory and is
used as removable storage.
● Because there are no moving parts and no removable media to
damage, this type of storage is very robust.
● The data stored on solid state backing storage is rewritable and
does not need electricity to keep the data.
○ Memory sticks/pen drives
○ Flash memory cards
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24. Memory Sticks / Pen Drives
● Memory sticks/pen drives are very popular storage media which
offer large storage capacities and are ideal media for
photographs, music, and other data files.
● Memory sticks are more expensive per Gb than CD/DVD/hard
disks.
● They consist of printed circuit boards enclosed in a plastic case.
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25. Memory Sticks / Pen Drives
The main advantages are:
● Small and lightweight - easy to put on your key ring or in your pocket.
● Can be used in almost any computer with a USB drive.
● Large storage capacity (up to 256Gb).
● No moving parts so they are very reliable.
● Not subject to scratches like optical media.
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26. Memory Sticks / Pen Drives
The main disadvantages are:
● Their small size means they are easily stolen.
● They are often left in the computer by mistake and lost.
● They have lower access speeds than a hard disk.
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27. Flash Memory Cards
● Flash memory cards are the small thin rectangular or square
removable cards that are used for storage of digital images by
digital cameras.
● They can also be used in any situation where data needs to be
stored and so are used with desktop computers, laptops, mobile
phones, and MP3 players.
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28. Back ups and reasons for taking
● Abackup is a copy of data and program files kept for security reasons. Should the originals be
destroyed or corrupted then the backups can be used.
● Using a file server and storing both programs and data on it means that backups can be taken in
one place.Backups should be held on removable devices or media that are taken off site each
day.
● The individual users do not need to take their own backups.The person in charge of the
network (usually the network manager) will take the backups needed.
● Many systems now take backups automatically at a certain time of the day and send the data
using the internet to a company that specialises in storing backups.
● Backups should always be removed off-site.This is incase of fire or if the building is destroyed.
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