66 CHAPTER SYSTEM UNIT

© 2005 The McGraw-Hill Companies, Inc. All Rights Reserved. 1-2 Announcement: Major Exam 01 Thursday, 17th March, 2005 Building 10 6:00pm Contents: Lecture Slides: #2 to #9 (all topics) Text Book: Chapter 1 (all pages), Chapter 2 (page )

© 2005 The McGraw-Hill Companies, Inc. All Rights Reserved. 1-3 Announcement: Lab Exam 01 Lab #6 Building 24/ 278 Contents: Lab Practices: #2 to #5 (all topics) Home works: #1 to #5 Lab Book: Microsoft Excel (Chapter 1 – 4)

© 2005 The McGraw-Hill Companies, Inc. All Rights Reserved. 1-4 Lecture Objectives Internal Data Representations How Numbers are represented? How Characters are represented? How Instructions are represented? Character Coding Schemes ASCII/ EBCDIC/ UniCode

© 2005 The McGraw-Hill Companies, Inc. All Rights Reserved. 1-5 Internal Data Representation Numeric representation & calculation Decimal Vs Binary number systems Conversions (Decimal to Binary and vice versa) Why binary in computers? Easy to represent using voltage levels Easy to implement binary operations using transistors (adder/divider circuits etc.) Binary Addition Examples Definitions Bit Byte

© 2005 The McGraw-Hill Companies, Inc. All Rights Reserved. 1-6 …..Internal Data Representation How to do binary – decimal conversions? Decimal to Binary Needed when something goes in (from keyboard etc.) Conversion Example: 10 in decimal is 1010 in binary. (Divide 10 repeatedly by 2 and note down the remainders in reverse order) Binary to Decimal Needed when something comes out (to Screen etc.) Conversion Example: 1010 in binary is 10 in decimal. Multiply each digit with its corresponding power of 2. Add all products at the end.

© 2005 The McGraw-Hill Companies, Inc. All Rights Reserved. 1-7 …..Internal Data Representation How to represent characters? Coding Schemes Binary coding schemes ASCII – 8 bit code EBCDIC -8 bit code Unicode – 16 bit code Coding ranges 8 bit – 256 codes 16 bit – codes

© 2005 The McGraw-Hill Companies, Inc. All Rights Reserved. 1-8 …..Internal Data Representation How a character goes into memory? Advantage of standard coding –Coded data can be shared across different systems –Problems: Microcomputer (ASCII) Mainframe (EBCDIC) –Solution: Conversions are done by special middle layer programs.

© 2005 The McGraw-Hill Companies, Inc. All Rights Reserved. 1-9 Binary Codes ASCIImicrocomputers Unicodeinternational languages

System Board Allows I/O devices to communicate with the system unit.

© 2005 The McGraw-Hill Companies, Inc. All Rights Reserved System Board The board which makes possible the inter connection of all computer components. Every system unit component has a direct connection with this board. Provides wires (data path) in between components.

© 2005 The McGraw-Hill Companies, Inc. All Rights Reserved The Microprocessor chip The brains of the whole system Composed of Control Unit Arithmetic Logic Unit (ALU) Control Unit sends control signals to the rest of the devices like Memory – reading/writing for instructions/data/results Arithmetic Logic Unit Other external devices – for input/output etc.

© 2005 The McGraw-Hill Companies, Inc. All Rights Reserved. 1-13