Digital Representation.ppt

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1、Oct 13,fit100-08-digital,1,Digital Representation,INFO/CSE 100, Fall 2006 Fluency in Information Technology,http:/courses.washington.edu/info100/,Oct 13,fit100-08-digital,2,Readings and References,Reading Fluency with Information Technology Chapter 8, Bits and the “Why“ of Bytes,Oct 13,fit100-08-dig

2、ital,3,Info Representation,Digitization: representing information by any fixed set of symbols decide how many different items of information you want to represent Tic Tac Toe: 2 items - player 1 or player 2 decide how many “digits“ or positions you want to use Tic Tac Toe: 1 position - a board squar

3、e, 9 squares total decide on a set of symbols player 1: player 2: ,Oct 13,fit100-08-digital,4,Are two symbols enough?,We can represent each players move this way, but what about representing the whole game?,Oct 13,fit100-08-digital,5,Empty position: ,Now we can represent this game as one 9-digit len

4、gth string: How many possible game states are there? 333333333 = 39 = 19,683,use this set of symbols empty cell: player 1: player 2: ,Oct 13,fit100-08-digital,6,Another encoding,Now we can represent this game as one 9-digit number:2 0 0 1 1 2 0 0 0 How many possible game states are there? 333333333

5、= 39 = 19,683,use a different set of symbols empty cell: 0 player 1: 1 player 2: 2,Oct 13,fit100-08-digital,7,Info in the Physical World,Physical world: Present and Absent (PandA) The most fundamental representation of information is presence/absence of a phenomenon,Any controllable phenomenon works

6、: define it right,Oct 13,fit100-08-digital,8,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,0,0,1,0,Oct 13,fit100

7、-08-digital,9,Lets Raise our Hands,Oct 13,fit100-08-digital,10,Connect Physical/Logical,The power of IT comes from the fact that physical and logical worlds can be connected,Present represents true / Absent represents false,- or maybe vice versa -,Memory,false true false false false true true false

8、true false true false false false,0 1 0 0 0 1 1 0 1 0 1 0 0 0,Oct 13,fit100-08-digital,11,Bits,PandA is a binary representation because it uses 2 patterns Tic Tac Toe had 3 patters and thus was not binary The word “bit“ is a contraction for “binary digit” represents a scenario being set and detected

9、 in 2 patterns,Oct 13,fit100-08-digital,12,Possible Interpretations of Bit Patterns,Oct 13,fit100-08-digital,13,Assigning Symbols for Characters,26 uppercase and 26 lowercase letters in English, plus 10 digits, plus 20 basic punctuation characters = 95 distinct charactersRepresenting this many chara

10、cters in binary takes 7 bits! 26 (6 bits) gives 64 symbols 27 (7 bits) gives 128 symbols7-bit code for characters is ASCII (American Standard Code for Information Interchange),Oct 13,fit100-08-digital,14,8-bit ASCII,0100 0110 0100 1001 0101 0100,More hands!,Oct 13,fit100-08-digital,15,Bytes,A byte i

11、s eight bits treated as a unit Adopted by IBM in 1960s A standard measure until very recently Bytes encode the Latin alphabet using ASCII - the American Standard Code for Information Interchange,0100 0110 0100 1001 0101 0100,How many bytes?!?,Oct 13,fit100-08-digital,16,Unicode,Although 8-bit ASCII

12、is widely used, there is a problem! Cant support more than 256 characters This eliminates more than half of the worlds language from the character set Unicode is a 16-bit representation Supports 65,536 symbols Can handle all languages,0100 0110 0000 1001,Oct 13,fit100-08-digital,17,HTML Encoding,8bi

13、t ASCII : 256 Characters16bit Unicode: 65,536 Characters ,Oct 13,fit100-08-digital,18,So Everything can be a 1 or a 0?,A Chair can be a 1 or 0? Letters C H A I R - ASCII Code - 1/0 Description of chair in words How advanced can we get? Picture of the chair 1/0s? Movie of the chair? Interactive 3D mo

14、del of the chair?,Oct 13,fit100-08-digital,19,Summary,IT joins physical & logical worlds Symbols represent things 1-to-1 Create symbols by grouping patterns PandA representation is fundamental presence and absence Can be represented in binary Bit, a place where 2 patterns set/detect ASCII is a byte encoding of Latin alphabet,