AS Level ICT

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AS Level ICT

• Selection and use of storage requirements, media,
  and devices Devices and media

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Primary and Secondary storage

• The two means of storing programs and data in a
  computer system are
• Primary storage this is storage that uses chips
  within the control, arithmetic, and logic units
• Secondary storage also know as backup storage,
  this is uses media that is outside the control,
  arithmetic, and logic units

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Secondary storage

• Secondary storage is important because it allows
  users to
• Ensure that data is stored safely and securely so
  that it can be accessible at a later date
• Transfer data from one computer to another

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Secondary storage

• There are a range of different devices that can
  be used as secondary storage including
• Magnetic disk drives
• Optical drives
• Magnetic tape drives
• Solid-state storage (Flash/Pen drives and Memory
  Card drives)

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Magnetic disk drives

• Magnetic disk drives come in two different media
• Floppy drives these use floppy disks
• Hard drives (also known as Hard Disks)

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Floppy drives

• Floppy disks are a removable media that fit into
  floppy drives
• The original floppy disk was produced in 1969 by
  IBM
• It was 8 inches across, and could store 80
  kilobytes of data
• It was replaced in 1975 by the 5.25 inch floppy
  disk

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Floppy drives

• These were, in turn, replaced in 1984 by the 3.5
  inch floppy disk
• This is a flexible plastic disk, coated with a
  magnetic layer, within a hard plastic protective
  outer cover
• A sliding metal cover protects the magnetised,
  plastic disk when it is not in the floppy disk
  drive
• Floppy disks originally held 360 kilobytes, but
  the latest versions can store 1.44 megabytes

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Floppy drives

• Because the demands for large, portable storage
  media has grown considerably since the
  introduction of the 3.5 inch floppy disk, it is
  now reached the end of its life as a viable,
  large-scale storage media
• Many computers are now being sold without floppy
  drives and it is likely that it will soon become
  a museum piece like its predecessors

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Hard drives

• Hard drives are also sometimes referred to as
  hard disks
• Hard drives consist of a series of rigid plastic
  disks, each of which is covered with a magnetic
  surface
• A hard disk spins at a speed of between 60 and
  120 revolutions per second
• The data stored on the hard disk is read or
  written by a head that floats just above the disk
  (less than 0.1mm!) on a cushion of air

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Hard drives

• Because the head is so close to the surface of
  the hard disk, even a dust particle can cause the
  head to crash into the surface
• To stop this happening, hard disks are always
  kept inside sealed units

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Hard drives

• The surface of a hard disk is divided up into
  Sectors and Tracks
• Data is stored in the blocks created by the
  Sectors and Tracks
• Moving data into a block is called Random Access

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Hard drives

• Hard drives have the major advantages of having
• A very high transfer rate
• A very large storage capacity
• Internal hard drives can also be added to
  existing computers in order to increase their
  storage capacity, and external hard drives
  often connected via a USB can be used as both
  additional storage and as a removable backup media

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Optical drives

• Optical disks are a removable media that fit into
  optical drives
• They are flat circular disks that are covered
  with surface that can be burned with a laser to
  create prismatic bumps
• The bumps are used to store data
• The bumps can then be read by a light beam
  that reflects from the bumps
• A read/write optical drive contains the laser
  that burns the optical disk and the light beam
  that reads it

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Optical drives

• There are a variety of different optical disks
  available
• CD-ROM Compact Disk Read Only Memory
• CD-R Compact Disk - Recordable
• CD-RW Compact Disk - Rewriteable
• DVD Digital Versatile Disk
• DVD-ROM Digital Versatile Disk Read Only
  Memory
• DVDRW Digital Versatile Disk Read/Write

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Compact disk CD-ROM

• This is the most common type of CD available, and
  is the way in which most modern software is
  supplied to individual personal computers
• With CD-ROMs
• Data is read only
• Data is stored as an optical pattern on the
  surface of the disk
• Storage capacity is 600 megabytes
• Can used for the distribution of software

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Compact disk CD-R

• These are supplied blank and can be written
  to by CD-Writer drives
• They can be used to store large amounts of data,
  but once used, they can not be re-used
• They are ideal for use as a backup storage media
  or to store digital music

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Compact disk CD-RW

• These are supplied blank and can be written
  to by CD-Writer drives
• They can be used to store large amounts of data,
  and can be written to many times, just like a
  hard drive
• However, the transfer rate is slower than that of
  a hard drive, and it is not as robust

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Digital versatile disk

• The DVD was originally called the Digital Video
  Disk, but once it was realised how much data they
  could to store, the name was changed to reflect
  the disks versatility
• The DVD is now replacing the CD as the main
  method of bulk saving data on personal computers
• The reason for this is that they are capable of
  storing much larger amounts of data
• A DVD can store 17 gigabytes of data this is
  equal to 26 CD-ROMs or 12,000 floppy disks!

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Digital versatile disk DVD-ROM

• These are mainly used for the distribution of
  movies
• DVD-ROM drives can read CD-ROMs

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Digital versatile disk DVDRW

• These are supplied blank and can be written
  to by DVD-RW and DVDRW drives
• The difference between the two types of
  rewriteable DVD is in the dye used on the surface
  of the DVD
• DVD-RW can be read by all DVD drives, but DVDRW
  can only be read by the more modern DVD drives

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Digital versatile disk DVDRW

• Older DVDs have a storage capacity of 4.7
  gigabytes whereas the latest ones can store up to
  8.5 gigabytes

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Disk access time

• Disk access time is sometimes used to describe
  the speed at which different drives can access
  information.
• It is defined as the amount of time it takes for
  the drives head to reach the correct block on
  a disk so that the data that has been selected
  can be accessed
• This can take up to 15 milliseconds for a hard
  disk and longer for other disk media

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Magnetic tape drives

• Magnetic tape drives store data on plastic tape
  that is coated with a magnetic surface
• The tape is then stored on a reel or within a
  cartridge/cassette
• It is a cheap method of storing large amounts of
  data that does not need to be accessed quickly
• As a result, it is often used as a backing
  store for large and mainframe computers

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Magnetic tapes Reel-to-reel
Reel-to-reel magnetic tape in use with a large or
mainframe computer
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Magnetic tapes Cartridge/cassettes
A 400 gigabyte magnetic tape data cartridge or
cassette This would primarily be used a backup
storage for a large or mainframe computer
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Solid-state storage

• The use of solid-state storage devices (i.e.
  devices that use memory chips) in removable media
  has grown considerable over recent years
• The two most common solid-state storage devices
  in use are
• Flash/pen drives (also known as USB memory sticks
  or thumb drives)
• Memory cards

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Flash/pen drives

• These have become very popular because they are
  cheap, portable, and have a reasonably large
  storage capacity (typically 1 to 8 gigabytes)
• They are a printed circuit board encased in a
  protective plastic case, and they interface with
  a computer via a USB connector

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Flash/pen drives - Advantages

• The main advantages of flash/pen drives are
• They are small and lightweight
• They can interface with any computer that has a
  USB connector
• They can store relatively large amounts of data
• They are reliable as they have no moving parts
  that can break
• It is very difficult to damage data that is
  stored on a flash/pen drive

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Flash/pen drives - Disadvantages

• The main disadvantages of flash/pen drives are
• They can be easily lost or stolen
• They have a slower transfer rate than a magnetic
  hard drive

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Memory cards

• These have become very popular as a storage media
  for use with digital cameras although they can be
  used to store any digital data
• They are a printed circuit board encased in a
  protective plastic case, and they interface with
  a camera or computer via a special connector
• They are very lightweight but must always be kept
  in a protective box when not in use as the
  special connectors can easily be damaged

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Memory cards

• Examples of the different types of memory cards
• These include
• CompactFlash (CF Card)
• Secure Digital Card (SD Card)
• MultiMediaCard (MMC)
• Sony Memory Sticks
• SmartMedia
• xD-Picture Card

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AS Level ICT

• Selection and use of storage requirements, media,
  and devices Devices and media