2024-03-04

Introduction

Summary

keywords

TODO

HW

Exercise*

Next time

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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.

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Zoned formats

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