The Computer: A Digital Tool

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The Computer A Digital Tool
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The computer

• A computer is a computationally complete system
  - capable of solving all of the problems that can
  be solved algorithmically. To be practically
  applicable, however, it not only has to be
  complete, but to be fast and reliable as well.
  The electronic computer serves this purpose by
  means of digital technology.
•  

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Digital Technology

• Based upon bi-stable electronic components
• Always in 1 of 2 states conventional to
  represent these states using digits 0 and 1
• Relationship between electronic
• components and the binary number system.

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Binary system (1)

• Uses only two digits 0 and 1, to represent
  numbers.
• Larger numbers are represented as sequences of
  digits, in which each position in the sequence is
  associated with a different weight.

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Binary system (2)

• This sequence of digits 10100011 represents the
  number 163

Digit sequence 10100011 Value of digit sequence
12803200021 163
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Binary system (3)

• A single Binary digIT is called a bit. In
  practice, the circuits of contemporary computers
  are commonly based upon sequences of 8 bits,
  called bytes. The largest value that can be
  represented by a single byte is 255 (digit
  sequence 1 1 1 1 1 1 1 1)

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Binary system (4)

• Try working out the sequences that give you a
  value of
• (i) 162
•  (ii) 97

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DIGITAL STORAGE THE COMPACT DISC (CD)
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CDs

• Most cost-effective method available today of
  storing and distributing multimedia applications
• Introduced in 1981 to store music could play
  high-fidelity music over and over
• Also able to hold digital data became computer
  storage device
• First CD-ROMS slow and expensive data transfer
  from CD to computer was 1X (150 KB/sec) now 12X
  available (1800 KB/sec)

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CD Format

• An optical device read by a laser beam
• (vs. magnetic device like hard disk/floppy disk
  or diskette)
• Some types of compact disc that hold different
  data formats
• CD-DA (CD-Digital Audio)
• CD-ROM
• CD-R (CD-Recordable)
• VideoCD
• CD-RW

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CD-ROM (CD-Read Only Memory)

• Most widely used format
• Holds digital data that can be read by different
  computers with a CD-ROM drive, with appropriate
  platform
• Hybrid CDs playable on multiple platforms

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CD Physical attributes

• Diameter of 12 cm 1.2 mm thick weighs 14 33
  grams hole at centre 15 mm in size  
• Made of plastic, with layer of aluminium
• One side for data, one side for label

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Data storage on a disc

• A CD-ROM stores in pits and lands
•  
• A pit disperses light
• A land reflects light
•  Light reflectability forms the binary digits 1
  and 0 that a computer needs to process data
•  The more data, the more pits and lands

CD Surface
Pit
Pit
Land
Land
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Advantages of CD-ROM

• Availability of large installed-base easy
  distribution  
• Large storage capacity average CD-ROM holds 650
  MB of data (gt 470 1.44 MB floppy disks)
• Able to play audio and video
• Read-only medium data can be read, not written
  to
• ð Immune to viruses
• ð Cannot be erased
• ð  Durable lifespan of 100 years
• ð Cannot crash like hard drive surface does
  not wear
•  

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Disadvantages of CD-ROM

• Can only read data cannot be updated or changed
   
• Duplication copies will contain same
  (unerasable) problems
• Coasters editing and testing important
• Slow access time (compared to hard drive)
•