Data%20Representation

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Data Representation

• Bits Bytes

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Computers Speak Binary

• All data and software programs in a computer are
  in binary format

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Logical versus Physical View

• Logical View
• A
• As humans see it

• Physical View
• 0100 0001
• As computers see it

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Binary Digit

• Called a Bit
• Signifies one of two states
• On
• Off
• Represented by 0 1 (Base 2)
• Eight Bits One Byte

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Representing Character Data

• Computers use an encoding system to represent
  character data

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Encoding Systems
ASCII Unicode EBCDIC
American Standard for Information Interchange Extended Binary Coded Decimal Interchange Code
One Byte Two Bytes One Byte
256 possible characters 65,000 possible characters 256 possible characters
A 0100 0001 A 0000 0000 0100 0001 A 1100 0010
DOS and Windows to Windows 98 Windows NT, Windows 2000, Windows XP IBM Mainframe
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Representing Program Instructions

• All computer programs are stored in binary format
• Move 97 to register al 1011 000 0110 0001

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Representing Numbers

• Computers use base 2, to store numbers

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Base 2 Number System

• Decimal, base 10, uses ten digits 0-9
• Each position is 10 raised to a power
• Binary, base 2, uses two digit 0-1
• Each position is 2 raised to a power

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How Base 2 works
0 0 1 0 1 0 1 1
128s 64s 32s 16s 8s 4s 2s 1s
27 26 25 24 23 22 21 20
1 x 32 1 x 8 1 x 2 1 x 1 43
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Hexadecimal - Shorthand Binary
0 0000 0 8 1000 8
1 0001 1 9 1001 9
2 0010 2 10 1010 A
3 0011 3 11 1011 B
4 0100 4 12 1100 C
5 0101 5 13 1101 D
6 0110 6 14 1110 E
7 0111 7 15 1111 F
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Other Types of Data

• Images and sounds are stored using a combination
  of a header followed by data

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Images

• Number of Pixels
• Picture Element
• Smallest addressable position on a screen
• Image size in pixels
• Number of colors
• 8 bits - 256 colors
• 24-32 bits - millions of colors (true color)

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Sound (MP3)
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Determining What 0s and 1s Mean

• Data interpretation depends on file type
• File type determined by file extension

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File Extensions
.txt Text
.doc Word Processing Microsoft Word
.wps Word Processing Word Perfect
.xls Spreadsheet Microsoft Excel
.jpg Image
.bmp Image
.mp3 Sound
.wav Sound
.htm Web Page
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Bits Computer Hardware

• Bits are represented five different ways in
  computer hardware
• Representation can be volatile or non-volatile

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Integrated Circuits

• Electrical representation
• Multiple transistors on silicon chip
• Open - electricity can flow - 1
• Closed - no electrical flow - 0
• Volatile
• CPU
• Ram

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Wire Connections

• Electrical representation
• 1.8 volts (or greater) - 1
• 0 volts - 0
• Volatile
• System bus

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Magnetic

• Magnetic properties of iron oxide particles
  covering a surface
• Particles in one direction - 1
• Particles in opposite direction - 0
• Non-volatile
• Hard disk

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Optical

• Reflective surface with burned areas
• Burned - Pit -1
• Not burned - Land - 0
• Non-volatile
• CD
• DVD

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Solid State

• Trapped electrons in a grid pattern with gates
• Open - 1
• Closed - 0
• Non-volatile
• Flash Drive