DATA CODING

1
CHAPTER 7

• DATA CODING

I've Been Encoded, Encrypted and Zipped. How much
can one disk take
2
CODING

• A CODE IS A PREDETERMINED SET OF SYMBOLS THAT
  HAVE SPECIFIC MEANINGS
• A CHARACTER IS INDIVIDUAL LETTERS, DIGITS,
  PUNCTUATION MARKS, OR OTHER SYMBOLS
• CODES ARE ASSIGNED TO THE CHARACTERS AND WHEN
  ENTERED MEAN PRODUCE THE CHARACTER
• MORSE CODE IS ONE EXAMPLE OF AN EARLY BINARY CODE

3
MORSE CODE
DASH 1 DOT 0
4
MACHINE CODE

• CODE THAT ALLOWS COMPUTERS TO INTERACT WITH
  TERMINALS AND HUMANS
• MUST BE TRUE BINARY
• ALL CHARACTRES MUST HAVE THE SAME NUMBER OF BITS
• ALL BITS MUST BE PERFECTLY FORMED
• ALL BITS MUST BE OF THE SAME DURATION

0001 1 0010 2
5
BINARY CODE

• 1 0N STATE OR CURRENT FLOWING
• 0 OFF STATE OR NO CURRENT FLOWING
• ALL STATES OF 0 OR 1 HAVE A SPECIFIC MEANING

1010010
6
POWERS OF 2 CHART
7
CHARACTER ASSIGNMENTS

• ALPHANUMERIC CHARACTERS
• LETTERS, NUMERALS, SYMBOLS
• FORMAT EFFECTOR CHARACTERS
• POSITION CONTROL ON SCREEN
• CONTROL CHARACTERS
• HARDWARE CONTROL FOR DATA TRANSMISSIONS AND
  TERMINALS CONNECTED TO LINES. SEE PAGE 277 AND
  278 OF TEXT FOR THE MOST COMMON.

CAN YOU NAME SOME?
8
WHAT IS PARITY CHECKING?

• A PARITY BIT IS AN EXTRA BIT ADDED FOR CHECKING
  TO ENSURE THE TOTAL NUMBER OF 1BITS IS EVEN OR ODD

9
BAUDOT CODE
TELEGRAPH, TELETYPEWRITER, TELEX COMMUNICATIONS
FIVE BIT CODE
10
ASCII CODE

• AMERICAN STANDARD CODE FOR INFORMATION
  INTEREXCHANGE
• MOST WIDELY USED IN COMPUTERS
• 7 BIT CODE WITH 128 CODE POINTS
• ALL BINARY
• 96 GRAPHIC CHARACTERS
• 32 CONTROL CHARACTERS

11
ASCII CODE TABLE
12
EBCDIC CODE

• EXTENDED BINARY CODED DECIMAL INTEREXCHANGE CODE
• IBM CODE USED IN IBM MAINFRAME COMPUTERS AND
  OLDER TERMINALS
• 8 BIT CODE WITH 256 CODE POINTS
• CHART IS READ THE SAME AS ASCII CODE CHART

13
EBCDIC CODE TABLE
14
UNICODE

• IMPLEMENTED TO HANDLE ALL LANGUAGES ON EARTH
• 16 BIT CODE WITH 65,536 CODE POINTS
• IMPLEMENTED INTO WINDOWS NT, WINDOWS ME, AND
  WINDOWS XP
• THE EVENTUAL REPLACEMENT FOR ASCII AND EBCDIC

15
CODE EFFICIENCY

• DEFINED AS THE NUMBER OF INFORMATION BITS DIVIDED
  BY THE TOTAL NUMBER OF BITS IN A CHARACTER
• EXAMPLE AN 8 BIT CODE WITH ONE PARITY BIT IS
  CALCULATED AS 7/8 -.875 OR 87.5 EFFICIENT
• ASCII AND EBCDIC HAVE NO PARITY AND ARE 100
  EFFICIENT

16
CODE CONVERSION

• Necessary when two systems run on different code
• Most common conversion from ASCII to EBCDIC
• Depending on the code some characters may not be
  converted

17
3-BIT TO 4-BIT EXAMPLE
18
DATA COMPRESSION

• The process of reducing the number of bits used
  to represent a character or shortening the number
  of characters before transmission
• The concept behind utilities such as Winzip and
  Winrar
• Three major types of Data Compression
• Character Compression/Huffman Coding
• Run Length Encoding
• Character Stripping

19
TYPICAL COMPRESSION SETUP
20
DATA ENCRYPTION

• The transformation of meaningful code data to a
  meaningless sequence of digits and letters
• Receiver must be able to unscramble or decrypt
  the message
• Called Ciphertext
• Necessary to protect easily captured data

21
ENCRYPTION STANDARDS

• DES DATA ENCRYPTION STANDARD
• 64 bit encryption using a 56 bit key with 72
  Quadrillion possibilities
• Still vulnerable to modern computing power
• TRIPLE DES
• Doubles DES key length to 112 bits
• Signal is encrypted three times
• PKE PUBLIC KEY ENCRYPTION(RSA Security, Inc.)
• Key for encryption is public
• Key for decryption is private
• Almost impossible to break
• Used widely on the Internet for business