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Introduction

Summary

keywords

TODO

HW

Exercise*

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Information Representations

Tech in chronological order.​

  1. Mechanical
  • uses gears for moving.
  • physical representation of state : gears in a specific configuration.
  1. Electrical
  • our computers.
  • physical representation of state : voltage or no voltage state.
  1. Optical
  • optical computing is commercially on the horizon.
  • It is still too expensive.
  • physical representation of state : photon present or absent state.
  1. Quantum
  • completely different tech.
  • you change the data as you read. -> a finite state does not exist.
  • Instead, the computations collide into probabilities.

physical repr. are on binary information systems.

  • data implicit by some physical entity being present or not.

data representations​

Computer

  • binary. 1:4 compression is hexadecimal. 1:3 compression is octal(rarely used)

Human

  • sexagesimal :12 based system. advantages on exact fractions.
    • babilonian canaric symbol..

Concept and its representations.​

value is different from its representations. The concept is unisome; its presentation can be multiple.

example. number is represented in integer form and real number form( IEEE 754) inside computer.

  • negative numbers? : 1 bit for direction & other bits for magnitude?
  • 2's complement is a system to express value AND direction integrated at the same time.

character is represented in font(a graphic form), and hard coded to ASCII,EBCDIC,Unicode table. zoned ?

  • ascii and ebcdic is limited; it uses 8bit (=1byte) for each character repr.
  • unicode uses 16bit (=2byte) for each character repr.
  • korean is represented in unicode(2byte) converted into utf-8(3byte) and transmitted.

binary coded decimals are half way between number and character representations. BCD to character, BCD to decimals are easy.

sidenote. zero is technically not a value; it is more of a placeholder.

Zoned formats​

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