Backing storage media

Backing storage media
1.Definition
2. Use of backing storage devices
3. Advantages and disadvantages

 Without digital storage media like hard disks, cd’s, dvd’s, servers
and so on, your computer will be just like a standalone video
player, only processing digital signals and nothing more.
 These storage devices are non-volatile, meaning that they do not
require constant power to store information. Thus they are most
suitable for long term storage of information.
 On the opposite side are components like computer RAM where
memory storage is dynamic but used only temporarily to aid
processes.
 Most digital storage data devices are accessed sequentially, thus
there will be seek time and latency to access any data on the
devices.
 Of course there are other different kinds of storage devices, not
just those that store your photos, music and other digital data.

 Volatility
 Non-volatile memory
 Will retain the stored information even if it is not constantly
supplied with electric power. It is suitable for long-term
storage of information. Nowadays used for most of
secondary, tertiary, and off-line storage. In 1950s and
1960s, it was also used for primary storage, in the form of
magnetic core memory.
 Volatile memory
 Requires constant power to maintain the stored
information. The fastest memory technologies of today are
volatile ones (not a universal rule). Since primary storage is
required to be very fast, it predominantly uses volatile
memory.

Semiconductor-Electronic
 Semiconductor memory uses semiconductor-based
integrated circuits to store information. A semiconductor memory
chip may contain millions of tiny transistors or capacitors. Both
volatile and non-volatile forms of semiconductor memory exist. In
modern computers, primary storage almost exclusively consists
of dynamic volatile semiconductor memory or
dynamic random access memory. Since the turn of the century, a
type of non-volatile semiconductor memory known as
flash memory has steadily gained share as off-line storage for
home computers. Non-volatile semiconductor memory is also
used for secondary storage in various advanced electronic
devices and specialized computers.

 Electronic storage medium that uses low-power laser beams to
record and retrieve digital (binary) data. In optical-storage
technology, a laser beam encodes digital data onto an optical, or
laser, disk in the form of tiny pits arranged in concentric tracks
on the disk’s surface.
A low-power laser scanner is used to “read” these pits, with
variations in the intensity of reflected light from the pits being
converted into electric signals. This technology is used in the
compact disc, which records sound; in the CD-ROM (compact
disc read-only memory), which can store text and images as
well as sound; in WORM (write-once read-many), a type of disk
that can be written on once and read any number of times; and
in newer disks that are totally rewritable.
Optical storage media

Magnetic storage media
 Magnetic storage uses different patterns of magnetization on a
magnetically coated surface to store information. Magnetic storage is
non-volatile.
 The information is accessed using one or more read/write heads which
may contain one or more recording transducers.
 A read/write head only covers a part of the surface so that the head or
medium or both must be moved relative to another in order to access
data. In modern computers, magnetic storage will take these forms:
 Magnetic disk
 Floppy disk, used for off-line storage
 Hard disk, used for secondary storage
 Magnetic tape data storage, used for tertiary and off-line storage
 In early computers, magnetic storage was also used for primary storage
in a form of magnetic drum, or core memory, core rope memory, thin
film memory, twistor memory or bubble memory. Also unlike today,
magnetic tape was often used for secondary storage.

Storage Capacity
 Data can be stored either in the 'internal memory' or on a
'storage device'.
 The amount of data and instructions that can be stored is
measured in 'bytes'.
 One byte contains 8 bits (short for Binary Digit). This is the
smallest unit of data that can be stored. Each 'bit' is
represented as a binary number, either 1 or 0.
 A single keyboard character such as the letter A or T
takes one byte of storage.

Read Only Memory (ROM)
 ROM is a special kind of memory which stores the instructions
which the computer uses when it 'boots up' - the BIOS (basic
input output system). It allows it to check the type of hard disk
installed, the amount of RAM installed (see next page), the type
of CPU being used etc.
 Because the data is 'read only', it can be read but not changed
by the user.
 The ROM chip (although there may be more than one) is
attached to the Motherboard.
 The key thing to remember about ROM is that the data is not
erased when the computer is switched off - the data is stored
permenantly. This type of memory is called 'non volatile memory'


Random Access Memory (RAM)
 How many times have you worked for a whole lesson on
something which you were just about to save but then
the computer crashed or your mate 'accidentally'
switched it off. When you rebootrd and logged back in,
your work was gone forever.
 This was because your work was stored in RAM, or
'temporary memory'. It was fairly safe there while the
computer was working, but as soon as it was switched
off, everything disappeared. This type of memory known
as 'volatile memory'.
 As well as storing the data you are working on, RAM
also stores the modules that are needed to make your
applications work. For example, when you open up
Microsoft Word, you may notice a short delay while the
modules are loaded into RAM.

 RAM is also needed so that you can have
multiple windows open and so that you can
switch between them.
 However, if you have a lot of windows,
documents and different applications running,
you might find that your system starts to slow
down. This is because your RAM is full up and it
is having to decide what it needs to keep stored
in memory at any given time and what it can
release. If this happens to you a lot, you can
improve the performance of your computer by
installing extra RAM.
 Most computers are typically sold with 1-2 Gb of
RAM installed.

Hard Disk
 The hard disk is the main storage device in your
computer. It is a bit like a filing cabinet: all of your data
files and applications software are stored on it.
 The hard disk contains a number of metal platters which
have been coated with a special magnetic material. The
data is stored in this magnetic material. Thus, the hard
disk is known as a magnetic storage device.
 In order to access the data, the platters spin many
thousands of times a second and a magnetic read and
write head floats just above the surface of the platter.

 When you hear the term 'hard disk crash', this refers to
the read/write head crashing down onto the surface of
the hard disk. There is a risk every time this happens
that the data stored in the section just where the head
crashes might be damaged. That is why it is a bad idea
just to switch the computer off at the wall without shutting
it down properly.
 Hard disks are measured in Gigabytes. A typical hard
disk size will be around 120 Gb - 1 Terabyte.
 It is possible to also have an external hard disk which
can be plugged into the computer and used to back up
your data and then stored in a different place to keep it
safe.


 Advantages
 necessary to support the way your computer works
 large storage capacity
 stores and retrieves data much faster than a floppy disk or
CD/DVD
 Stored items are not lost when you switch off the computer
 Cheap on a cost per megabyte compared to other storage
devices
 Disadvantages
 Far slower to access data than ROM or RAM chips
 Hard disks can crash which stop the computer from working
 Regular crashes can damage the surface of the disk, leading to
loss of data in that sector
 The disk is fixed inside the computer and cannot easily be
transferred to another computer.

Floppy Disk
 Floppy disks are one of the oldest types of portable storage
devices still in use, having been around since the 1980s.
However, they are gradually becoming obsolete and some
manufacturers are now starting to build their PCs without floppy
disk drives.
 A floppy disk can store up to 1.44 Mb of data which is equivalent
to around 300 pages of A4 text. They used to be the ideal
storage device for transferring small files from home to
work/school or from one office computer to another. But
nowdays, many files contain graphics or WordArt and are larger
than the size of the floppy disk.
 Floppy disks are a magnetic storage device.
 All disks must be formatted before data can be written to the
disk. Formatting divides the disk up into sections or sectors onto
which data files are stored. In the past, the user would have to
format their own disks, but now they are sold pre-formatted.

 Advantages
 Portable - small and lightweight
 Inexpensive
 Useful for transferring small files between home and school
 Security tab to stop data from being written over
 Can be used many times
 Disadvantages
 Not very strong - easy to damage
 Data can be erased if the disk comes into contact with a
magnetic field
 Quite slow to access and retrieve data when compared to a hard
disk
 Can transport viruses from one machine to another
 Small storage capacity
 Many new computers don't have floppy disk drives

Zip Disks
 Zip disks are pretty much obselete now. However, they
were very popular as a backup medium before CD-RWs
were developed and became cheap enough for
everyone to use.
 Zip disks look similar to a floppy disk but are a little bit
thicker.
 Computers generally didn't come with a zip drive
installed, so you couldn't just use one in the same way
as a floppy disk. You needed a seperate plug in drive,
which was an extra expense.
 They can store around 100Mb of data - 70 times more
than a floppy disk.

 Advantages
 Stores more data than a floppy disk
 Compresses data, reducing the file size, so
more data can be stored
 Portable
 Disadvantages
 Almost obselete now
 Need a seperate zip drive to read the disk
 More expensive than floppy disks

Magnetic Tape
 The amount of work that you do on your computer at home can
easily be backed up onto a CD-RW or a memory stick. However,
many organisations, such as your school or an office, need to
back up large volumes of data each day. A CD-RW, DVD-RW or
flash memory sticks just would not be large enough for doing
this.
 Large organisations who need to back up their systems daily
tend to use magnetic tapes to store their data.
 Magnetic tape uses 'serial access' to find a piece of data. It
works in much the same way as a video tape that you might
have at home. To find a specific piece of data, you have to start
at the beginning of the tape and continue fast forwarding until
you get to the piece of data that you need. This makes it fairly
slow to find and retrieve data so it would not be much use to
store data that you needed to get hold of quickly.


 Advantages
 relatively cheap per megabyte of storage
 can store large amounts of data - over 100
Gb
 can be set up to do the back up overnight or
over the weekend
 Disadvantages
 serial access so can be quite slow to access
data
 need a special piece of equipment to record
and read the data on the tape

Compact Disks (CD)
 Compact Disks come in three main forms:
 CD-ROM - CD Read Only Memory. This means
that when you buy the disk, it already has the
data or program stored on it. You can read it, but
can't save to it. An example would be a music
CD that you buy from a shop.
 CD-WORM - CD Write Once Read Many. This
means that you are able to save to this disk one
time, so you can store your data or an
application on it of your choice. However, once
you have saved onto the disk once, you can
access the data many times but can't save onto
it again.

 CD-RW - CD Read Write. This means that you can save
data to your disk over and over again, just like you can
with a floppy disk.
 Compact disks are known as optical storage devices.
Data is burned onto the surface of the disk using a laser
beam in the CD drive. A laser beam is also used to read
the data stored on the disk.
 A typical CD can store around 650 Mb of data -
equivalent to 450 floppy disks. The entire contents of
four text based encyclopedias (no images) could be
stored on a single CD.

 Advantages
 Small and portable
 Very cheap to produce
 Most computers can read CDs. If there is no CD
drive, a DVD drive can usually read them
 Fairly fast to access the data - quicker than a
floppy disk or magnetic tape
 Disadvantages
 Fairly fragile, easy to snap or scratch
 Smaller storage capacity than a hard drive or
DVD
 Slower to access than the hard disk.

Digital Versatile Disk (DVD)
 DVDs are amongst the most common methods of copying
and backing up data at home.
 A DVD is similar to a CD in that it is an optical device and that
a laser is used to store the data and read the data.
 A single sided DVD can store about 4.7Gb of data. DVDs
which store data on both sides can hold over 9Gb of data.
 One problem with the DVD is that the different companies
which make them haven't agreed on a standard format.
Because of this, you will see various kinds of DVD disks for
sale: DVD-R, DVD+R, DVD-RW and DVD+RW. You have to
make sure that you buy the right kind of disk to go with your
DVD equipment.

 Advantages
 Very large storage capacity
 Sound and picture quality is excellent, making
them ideal for storing films with video and
sound.
 DVDs are now mass produced so they are
relatively cheap
 DVD players can read CDs
 Disadvantages
 DVDs do not work in CD drives
 There is no single standard of DVD
 They can be easily damaged by breaking or
scratching

Flash Memory
 Flash memory storage devices are typically
small, lightweight, removable and rewritable.
They consist of a small printed circuit board
which is encased in plastic or metal casing.
They usually have a removable cap which
covers and protects the part of the stick
which is inserted into a USB port.
 Memory sticks are available from 1 Gb up to
8 Gb

 Advantages
 They are more compact and portable than floppy disks or CDs/DVDs.
 They hold more data than a floppy disk and nowadays often more than
a CD.
 They are more reliable than a floppy disk because they have no moving
parts
 They are being developed with fashionable looking outer casings and
are almost becoming a 'fashion accessory' much in the way of a mobile
phone.
 Disadvantages
 At the moment, the cost per megabyte of storage is more expensive
than floppy disks, CDs or DVDs.
 They can be easily lost
 The metal part which is inserted into the USB port can be snapped off if
they are handled roughly

Blu-ray
 Blu-ray Disc (also known as Blu-ray or BD) is an optical
disc storage media format. Its main uses are high-
definition video and data storage. The disc has the same
dimensions as a standard DVD or CD.
 The name Blu-ray Disc is derived from the blue laser
(violet coloured) used to read and write this type of disc.
Because of its shorter wavelength (405 nm),
substantially more data can be stored on a Blu-ray Disc
than on the DVD format, which uses a red (650 nm)
laser.
 A dual layer Blu-ray Disc can store 50 GB, almost six
times the capacity of a double-dual layer DVD (or more
than 10 times if single-layer).

Backing storage media

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