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Bits and Bytes

Learn about the differences between ASCII and EBCDIC codes, how computers interpret symbols, and why not all files are ASCII files. Discover the history, usage, and practical implications of ASCII and EBCDIC coding schemes in computing.

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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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