Storage Devices and Media
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Objectives
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Understand the difference between
internal memory & backing storage
Be able to identify different types of
storage devices & media
Identify the uses, advantages &
disadvantages of different types of
storage devices & media
GCSE Information Technology
Difference between internal
memory & backing storage
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Internal memory is the memory that is occupied by the current
data and instruction being dealt with.
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Its contents are lost when the computer is turned off.
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Backing storage is the additional memory which is used to
store data & instructions that we may need to use again.
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Hard Disk & Drive
Floppy Disk & Drive
Optical Disk Drive
USB Storage Devices
Magnetic Tape
Its contents are NOT lost when the computer is turned off.
GCSE Information Technology
Difference between internal
memory & backing storage
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Internal memory, also known as Immediate
Access Storage (IAS) is:
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Small
Fast
Volatile
Backing storage is:
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Large
Non –Volatile
Not very fast to read from.
GCSE Information Technology
How do we measure the size
of memory?
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Storing an individual character such as a
letter, number or other character needs a
set amount of space called a
Byte
To store 1024 characters we need 1024
Bytes or 1Kilobyte (1Kb)
1 million bytes (or 1000Kb) is called I
Megabyte (Mb)
1000 Mb is called 1 Gigabyte (1Gb)
GCSE Information Technology
Hard disk drives
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The Hard Drive is the DEVICE which reads & writes
to the Hard Disk
The Hard Disk is the STORAGE MEDIA
It’s Magnetic media
Data is stored magnetically onto tracks on the disk
Disk rotates at high speed – passing under the
read/write heads
Read/write heads READ the data into main memory
and WRITE data back to the disk after it has been
dealt with
GCSE Information Technology
Hard disk drives
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Uses
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Advantages
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Stores software
Stores your data files
Large storage capacity
Stored items are not lost when the computer is
switched off.
Usually fixed inside the computer, so can’t get lost.
Disadvantages
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Slower than IAS
If the hard disk crashes the computer will not work &
you have lost your work!!!
GCSE Information Technology
Floppy disks & drives
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Uses
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Advantages
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To keep personal data
Keep extra copies of data
Can be carried with you
Disadvantages
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Limited capacity (typically 1.44Mb)
Unlikely to store your ICT coursework on one
disk
GCSE Information Technology
Zip Drives
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Zip drives are similar to
floppy drives because the
individual disks are
removable and portable but
they hold much larger
amounts of data
Typically between 100 MB
and 2 GB.
GCSE Information Technology
Optical disk drives
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CD Rom
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Uses
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Storing software
Reference material (multimedia)
Advantages
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Compact Disk Read Only Memory
Known as WORM devices Write Once Read Many times.
Data cannot be erased
Portable
Much larger capacity than floppy disks (about 650Mb)
Disadvantages
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Can get lost
Can’t write data to a CD Rom
Data access can be slower than a hard drive.
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Optical disk drives
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DVD
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Uses
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Storing high quality audio & video
Advantages
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Digital Versatile Disk
Data cannot be erased
Portable
Much larger capacity than floppy disks and CD Rom (about 4.7 Gb)
Disadvantages
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Can get lost
Can’t write data to a standard DVD
GCSE Information Technology
Optical disk drives
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CD Rewriter
Uses
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Advantages
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Back up software & data files
Copy music files
Portable
Can store much larger files than floppy disks
Disadvantages
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Can get lost
Can’t always be read in some Optical drives
GCSE Information Technology
Optical disk drives
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DVD Rewriter
Uses
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Advantages
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Back up software & data files
Copy video files
Portable
Can store much larger files than CD R’s
Disadvantages
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Can get lost
Can’t always be read in some Optical drives or DVD players
GCSE Information Technology
USB storage devices
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Recent development
Fits on a key ring
Smallest storage capacity is about
32Mb = about 22 floppy disks
1Gb versions now available
Is this the end of the floppy disk?
GCSE Information Technology
Comparing storage device
capacity:
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1 CD-ROM (650 MB) = 451 Floppy
disks (1.44 MB)
1 DVD (4.7 GB) = 7 CD-ROM's (650
MB)
Access speed
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Hard drive - 1000 KB/s
CD-ROM - 100 KB/s
Floppy disk - 36 KB/s
GCSE Information Technology
Storage used for back-ups
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Magnetic tape
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Comes in two forms; tape reels, and cassettes or
cartridges.
Large tape reels are used to make backup copies of
programs and data on large mainframe computers.
Cartridges are used to make backup copies of the
programs and data on personal computers and
networks.
The main advantage of using magnetic tape as backing
storage is that it is relatively cheap and can store large
amounts of data.
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Direct and serial access
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Floppy disks, hard disks CDs and USB
storage devices all allow direct access to
data.
Direct access means that the required data
can be found straight away without having to
read through all the data on the disk.
Magnetic tape allows only serial access to
data. To locate data on a magnetic tape it
has to be searched from the beginning until
the required data is found.
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File compression
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File compression software can be used to make
files smaller so that more data can be stored in the
same amount of space on backing store.
When a compressed file on backing store needs to
be used it must be decompressed.
This can be done using decompression software
or by setting files up to be self-extracting which
means that they can automatically decompress
themselves.
Winzip is an example of software that can be used
to compress and decompress files.
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