Syllabus Contents
 he syllabus says that you should be able to:
 describe common backing storage media and their associated devices:
 magnetic tapes,
 CDs (all types),
 DVDs (all types),
 DVD-RAM discs,
 HD DVD discs,
 Blu-Ray discs,
 hard discs,
 memory sticks,
 flash memory
 identify typical uses of the storage media, including types of access (e.g.
serial/sequential, direct/random) and access speeds;
 describe the comparative advantages and disadvantages of using different backing
storage media;
 define the term backup and describe the need for taking backups;
 describe the difference between main/internal memoryand backing storage, stating
the relative benefits of each in terms of speed and permanence.
Main Memory
Main memory (sometimes known as internal
memory or primary storage) is another name
for RAM (and ROM).
Main memory is usually used to store data
temporarily. In the case of RAM, it is volatile (this
means that when power is switched off all of the data in
the memory disappears).
Main memory is used to store data whilst it is
being processed by the CPU. Data can be put into
memory, and read back from it, very quickly.
Backing Storage
Backing storage (sometimes known as secondary
storage) is the name for all other data storage
devices in a computer: hard-drive, etc.
Backing storage is usually non-volatile, so it is generally
used to store data for a long time.
Backing up data
Backing up refers to copying files of stored data onto
separate storage medium in case of a problem with the
main storage medium.
The backups are often stored in a different place to the
current location.
Reasons for backing up data
 Data could be lost due to the failure of the original
device e.g a head crush, possible corruption of files
 Hackers could be responsible for corruption
 In case the files must be used while at the same time
protecting the original files
N.B Backing up data does not necessarily protect against
viruses.
Types of access
 Serial Access
 Direct access
Serial Access
In this system access to data starts at the beginning until
the required information is found. It is used mainly on
magnetic tape systems. Speed of access and order are not
important.
In magnetic tapes a new tape is required to update
information.Old information is merged with the new
data.
Direct Access
It is used with magnetic disks and optical media. The
computer uses a program to calculate the position where
data is stored and it is accessed directly. It is used in
applications where access speed is vital like online and
real-time process systems
When updating data the new data is written to the next
available location and the position recalculated.
Types of Backing Storage Media
Backing storage ensures that data is stored permanently
and can be accessed later. It can be internal or external.
 Magnetic
 Optical
 Solid state
Magnetic tapes
Made of thin strips of plastic coated with a magnetic
layer. It is fed through a read/write head. Data is stored
as magnetised bits and accessed sequentially.
Uses- Used when large storage capacities are required
and speed is not critical e.g batch processing cheques,
Utility bills, payrolls and backups.
Advantages
 Cheaper than other storage media
 Robust- encased in a cartridge
 Data transfer rate is fast
 Can easily be kept away from the computer
Disadvantages
 Access is slow
 Updating files requires a new tape
Fixed hard disks
Fixed inside the computer and has platters on which
data is written. It stores important programs on the
computer such as operating systems. They are used by
an program that requires fast access to data e.g realtime systems in robotics,rocket lauching, online
systems and on file servers
Advantages and Disadvantages




Advantages
Data transfer rate is fast
Data access times are fast
Large storage capacity
Disadvantages
They are fragile
Portable hard disks
They are similar to fixed hard disks and can be
connected and disconnected from a computer easily
Uses-They are used as backup media or for transferring
server software from one computer to another.
Advantages and Disadvantages
Similar to fixed hard disks but are slower when accessing
data and more expensive
Prep- Do notes on the remaining storage devices
Optical Backing Storage Media
They operate using a laser beam. It reads from and
writes to the disk. The disk is polycarbonate plastic
covered in reflective material. This is etched into using
a laser beam. The ‘pits’ formed represent the data.
CD ROMS/DVD ROMS
The main difference is their storage capacity. DVDs use a
shorter wave length of laser light than CDs.
They are used for applications which require the
prevention of the deletion of data.
List examples of uses.
Adv. And Disadv.
Adv
-DVDs hold more data than CDs
-CDs are cheaper
-Both are more robust than hard disks
Disadv
-Data transfer rates are slower for both CDs and DVDs
-Data access times are longer
CD Rs/DVD Rs
A laser beam causes spots on the dye to be heated up
and the reading process distinguishes between the
heated and unheated spots.
Used for home recordings of cds and dvds
Adv
-Cheaper
-Cannot be accidentally written over
Disadv
-Can only be recorded once
-Not all CD players can read CD Rs
CD RWs/DVD RWs
The recording surface is a metallic alloy layer. It can exist
in anamorphous state or a crystalline state
Adv
-Can be used more than once
-Different versions of files can be overwritten
Disadv
-They are expensive
-Files can be overwritten accidentally
DVD RAMs
This is a newer technology. Data is stored in concentric
tracks like magnetic media.
They have quicker access times and an in built data
check to ensure that data is written correctly.
Used in camcorders, archiving and general data storage.
Adv and Disadv
Adv
-They have a bigger storage capacity
-More durable
Disadv
-Not compatible with most DVD players
-Expensive
Blu-ray disks
They have the largest storage capacity: 25, 50 and 100 Gb.
They use a shorter wave length laser beam using light that
is close to the blue/violet spectra.
Uses-games consoles, camcorders, entertainment
Adv
-Large storage capacity
-Data transfer rates are high
-Access speeds are high
Disadv
-Expensive
-Problems with encryption techniques for preventing piracy
Minidisks
Uses magnetic and optical technologies for recording data.
One site is heated and the other side is magnetised. It can
be wrtten several times. The disk is permanently housed in
a cartridge.
Used in portable music players
Adv
-Can be recorded over many times
-Robust
Disadv
-Transfer rates are slower
-Hold less data
-Expensive
Solid State Backing Storage
They are made of silicon chips consisting of rows and
columns of cells. Each cell is made of two transistors
separated by a thin oxide layer. They have no moving
parts. The cell has a value of 1 or 0 depending on its
charge.
Memory Sticks or pen drives
Connected to a computer via the usb port. Used for
transporting files and software fixes.
Adv
-Compact, robust and do not need drivers to operate
Disadv
-Cannot be write protected
-More expensive/Gbyte of storage