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Bits and Bytes

Bits and Bytes. ASCII/EBCDIC. There was one other problem with bytes: Compatibility. Given the binary sequences:. Manufact. #1:. Manufact. #2:. Manufact. #3:. A. 0. +. 0000000. B. 1. -. 0000001. C. 2. *. 0000010. D. 3. ?. 0000011.   .   .   .

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Bits and Bytes

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  1. Bits and Bytes ASCII/EBCDIC • There was one other problem with bytes: • Compatibility Given the binary sequences: Manufact. #1: Manufact. #2: Manufact. #3: A 0 + 0000000 B 1 - 0000001 C 2 * 0000010 D 3 ? 0000011             6 v TAB 1111110 7 x CR 1111101 8 y LF 1111110 9 z FF 1111111 Manufacturers Interpreted them differently

  2. Bits and Bytes Which is the Correct Interpretation??? Each is equally Correct • 0000010 Could be either a ‘C’ OR a ‘2’ • The letter ‘C’ Could be pronounced either ‘cee’ OR ‘ess’ What’s the Solution ??? ASCII The American Standard Code for InformationInterchange

  3. Bits and Bytes Sample ASCII Codes: Binary Sequence Character Description . Value 0000000 0 NULL NULL/Tape feed             0000111 BEL Rings Bell 7 8 BS Back Space 0001000             0001101 13 CR Carriage Return             0011011 27 ESC Escape             0100000 32 SP Space             0110000 48 0 Zero 0110001 49 1 One             1000001 65 A Capital ‘A’ 1000010 66 B Capital ‘B’             1100001 97 a Lower Case ‘a’ 1100010 98 b Lower Case ‘b’

  4. Bits and Bytes A Preview of Things to Come: • For the first Exam Memorizethe Numeric Values for: • NULL Value: 0 • BEL (Ring The Bell) Value: 7 • BS (Backspace) Value: 8 • CR (Carriage Return) Value: 13 • ESC (Escape) Value: 27 • SP (Space) Value: 32 • The digits (0, 1, …, 9) • NOTE: The Digit 0 (zero) has the value: 48 • The Uppercase Alphabet • NOTE: The Character ‘A’ has the value: 65 • The Lowercase Alphabet • NOTE: The Character ‘a’ has the value: 97

  5. Bits and Bytes Are We limited to only 128 (= 27) characters ?? Yes and no: • The STANDARD ASCII Character Set Consists of 128 Characters (as given in Addendum 1.1) There is an EXTENDED ASCII Character set which uses ALL 8-bits (1-byte) available (parity is NOT an issue) • The extended ASCII Character set consists of 256 (= 28) characters (See Addendum 1.2) • The Majority of the characters included in the extended ASCII character set are extensions of the Greco-Roman Alphabet (e.g., ß, Ü, å) or ‘graphics’ characters (e.g., )

  6. Bits and Bytes What does the term ‘ASCII file’ Mean ?? An ASCII File assumes that every 8-bits (1-byte) in the file are grouped together according to the ASCII tables Aren’t ALL Files ASCII Files ?? NO - As we will see later, not all data is stored according to ASCII formats That Helps (sort-of) to explain why when we display non-ASCII files we sometimes get characters such as ,  , , , , and 

  7. Bits and Bytes Do ALL computers use ASCII to Represent Symbols??? NO - Although most do. IBM had the first Coding Scheme (dating back to 1880) EBCDIC ExtendedBinaryCodedDecimalInterchangeCode EBCDIC is still used in IBM Mainframes and to store data on large reel-to-reel Tape Drives

  8. This Concludes The Slides for this Section Choose an Option:  Repeat Slides for this Section  Go To Slide Index For Chapter 1  Go To Slide Index For Chapter 2  Go To Slide Index For Textbook  Go To Home Page

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