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Ch. 8: Bits and Bytes
[^] Chapter Outlines
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<<Ch. 5: Web Searching Ch. 11: Multimedia Encoding>>
  1. Coding with symbols.
    1. Symbols are used to represent things.
    2. Numbers are convenient, but we could use others.
      601 925 3815, or ^)! (@% #*!%
    3. Ordering.
      1. Symbols made of digits are easily ordered for searching.
      2. We can do this with any symbols if we agree on the collating sequence.
      3. Alphabetical order is a collating sequence.
    4. Combining symbols.
      1. Symbols can be combined.
      2. If you have p symbols, a group of n gives you pn.
      3. Six faces on a die, two dice, give 62 = 36 pairs.
      4. Ten digits, 103 = 1000 3-digit numbers (including 000).
      5. If labels are constructed using five capital letters, there are 265 = 11,881,376 possible labels.
  2. Binary
    1. Information must be coded some physical phenomenon.
    2. Easiest to represent two states. Present and Absent: PandA.
      1. On or off.
      2. Charged or discharged.
      3. Magnetized or not.
      4. Pit or land (non-pit).
    3. Divide disks into areas.
    4. Hexadecimal
      1. A more compact representation for strings of bits.
      2. Use 16 symbols, 0–9, A–F: hex “digits”.
      3. Each hex digit is four bits:
        00000100012001030011
        40100501016011070111
        8100091001A1010B1011
        C1100D1101E1110F1111
      4. Group starting at right; pad with zeros on the left.
      5. 101000001010110011 is 282B3
      6. 37D1 is 0011011111010001.
  3. Encoding text.
    1. Each character is coded in ASCII.
      1. Originally, 7 bits, 0000000–1111111 (00–7F).
      2. PC expanded to 8, 00–FF. Second bank, 80–FF is not very standard.
      3. Tom is 010101000110111101101101, or 546F6D
    2. Other information is recorded using tags.
      1. HTML is one way; many others.
      2. Can think of < as an escape character.
<<Ch. 5: Web Searching Ch. 11: Multimedia Encoding>>