Notes

Outline

Announcements Midterm on Monday: Chapters 1-5,7,8

Digital Representation Everyone knows computers use  bits and bytes … but what are they?

Info Representation Digitization: representing information by any fixed set of symbols

Creating Symbols Usually there are not enough symbols The solution is to create more symbols by composing patterns … Three patterns alone could be symbols, but grouping them together makes 9 when they are pairs, 27 as triples, and ...

An Encoding Encode the Latin alphabet

Info in the Physical World Physical world: The most fundamental representation of information is presence/absence of a phenomenon matter, light, magnetism, flow, charge, … detect: “Is the phenomenon present?” set: make phenomenon present or absent

Info in the Logical World Logical World: Information, reasoning, computation are formulated by true/false and logic All men are mortal Aristotle is a man Aristotle is mortal True and false can be the patterns for encoding information

Connect Physical/Logical The miracle of IT is that physical and logical worlds can be connected

Bits PandA is a binary representation because it uses 2 patterns Bit -- it’s a contraction for “binary digit” -- a position in space/time capable of being set and detected in 2 patterns

Bytes A byte is eight bits treated as a unit Adopted by IBM in 1960s A standard measure ever since Bytes encode the Latin alphabet using ASCII -- the American Standard Code for Information Interchange

Demonstration I need 8 volunteers, 4 women & 4 men

Encoding Information Bits and bytes encode the information, but that’s not all Tags encode format and some structure in word processors Tags encode format and some structure in HTML In the Oxford English Dictionary tags encode structure and some formatting

OED Entry For Byte

Summary IT joins physical & logical domains so physical devices do our logical work  Symbols represent things 1-to-1 Create symbols by grouping patterns PandA representation is fundamental Bit, a place where 2 patterns set/detect ASCII is a byte encoding of Latin abet In addition to content, encode structure