1. Computer Systems Organization CS 1428 Foundations of Computer Science

2. 2 Objectives In this section, you will:  Review binary data representation  Put all the pieces together – the Von Neumann architecture Why getting more memory will help your computer run faster  Learn how C++ programs are run by the computer

3. Software  Programs are stored in a binary format that is specific to the processor (or virtual machine, in the case of Java)  High-level language programs must be “compiled” into machine language that is targeted toward a specific processor or operating system 3

4. From a High-level Program to an Executable File Slide 1- 4 Source Code Preprocessor Modified Source Code Compiler Object Code Linker Executable Code

5. 5  Representing integers Decimal integers are converted to binary integers Given k bits, the largest unsigned integer is 2 k - 1  Given 4 bits, the largest is 2 4 -1 = 15 Signed integers must also represent the sign (positive or negative) Integers often represented in two’s complement Binary Representation of Numeric and Textual Information

6. 6  Characters are mapped onto binary numbers ASCII code set  8 bits per character; 256 character codes  What is the numeric code for a capital A? In binary? UNICODE code set  16 bits per character; 65,536 character codes  Text strings are sequences of characters in some encoding Binary Representation of Numeric and Textual Information (continued)

7. 7  Representing real numbers Approximations  Not possible to store all real numbers Real numbers may be put into binary scientific notation: a x 2 b  Example: 101.11 x 2 0 Number then normalized so that first significant digit is immediately to the right of the binary point  Example:.10111 x 2 3 Mantissa and exponent then stored Binary Representation of Numeric and Textual Information (continued)

8. 8 Representing other data  Almost any analog information can be “digitized” to store on a computer Sound Pictures Video

9. 9 The Components of a Computer System  Von Neumann architecture has four functional units: Memory Input/Output Arithmetic/Logic unit Control unit  Sequential execution of instructions  Stored program concept

10. 10 Components of the Von Neumann Architecture Bus Cache

11. 11 Memory and Cache  RAM (Random Access Memory ) Memory made of addressable 8 bit “cells” Memory address  Unsigned binary number N bits long  Address space is then 2 N cells Fetch/store controller  Fetch: retrieve a value from memory  Store: store a value into memory

12. 12 Memory and Cache (continued)  Memory register Very fast storage location Given a name, not an address Serves some special purpose Modern computers have dozens or hundreds of registers

13. 13 Cache Memory  Memory access is much slower than processing time  Faster memory is too expensive to use for all memory cells  Locality principle Once a value is used, it is likely to be used again  Small size, fast memory just for values currently in use speeds computing time

14. CPU  Control Unit Manages execution  Arithmetic and Logic Unit (ALU) Does calculations 14

15. 15 The Control Unit  Manages stored program execution  Task Fetch from memory the next instruction to be executed Decode instruction: determine what is to be done Execute instruction: issue appropriate command to ALU, memory, and I/O controllers Decode Execute Fetch Instruction Cycle

16. 16 Control Unit Registers And Circuits  Parts of control unit Links to other subsystems Instruction decoder circuit Three special registers:  Program Counter (PC) Stores the memory address of the next instruction to be executed  Instruction Register (IR) Stores the code for the current instruction  Accumulator (ACC) Where the results of all arithmetic operations and loads is stored.

17. 17 The Arithmetic/Logic Unit  Actual computations are performed  Primitive operation circuits Arithmetic (ADD, etc.) Comparison (CE, etc.) Logic (AND, etc.)  Data inputs and results stored in registers  Multiplexor selects desired output

18. 18 Machine Language Instructions  Can be decoded and executed by control unit Always in binary!!  Parts of instructions Operation code (op code)  Unique unsigned-integer code assigned to each machine language operation Address field(s)  Memory addresses of the values on which operation will work

19. 19 Machine Language Instructions (continued)  Operations of machine language Data transfer  Move values to and from memory and registers Arithmetic/logic  Perform ALU operations that produce numeric values

20. 20 Machine Language Instructions (continued)  Operations of machine language (continued) Compares  Set bits of compare register to hold result Branches  Jump to a new memory address to continue processing

21. 21 Pippin View Assembly language (Closer to Human Language) Machine Language (Only thing a computer understands.) Copyright Notice Copyright Notice ©2003 PWS Publishing Company, All Rights Reserved.PWS Publishing Company

22. 22 Program: LOD #00000011 ADD 10000000 STO 10000011 HLT Note the error in the documentation. The STO op code is really 0000 0101.

23. 23 Summary  Computer organization examines different subsystems of a computer: memory, input/output, arithmetic/logic unit, and control unit  Machine language gives codes for each primitive instruction the computer can perform, and its arguments  Von Neumann machine: sequential execution of stored program