Copyright © 2003 by Prentice Hall Module 5 Central Processing Unit 1. Binary representation of data 2. The components of the CPU 3. CPU and Instruction set 4. Important features of CPUs

2Module 5: CPU Data representation All modern digital equipment work on binary digits, i.e., 0, 1, based on the two states of a circuitry, e.g. High voltage (ON): 1 Low voltage (Off) : 0 Why? Simple, reliable, and available technology CPU can only understand 0 and 1 Data must be represented in binary form before it is processed by a CPU How to representation number? How to representation number? Binary (base 2) number, containing only two digits, 0 and 1 Binary (base 2) number, containing only two digits, 0 and 1 How to represent characters? How to represent characters? English text for example

3Module 5: CPU Binary number In decimal (base 10) we indicate place values by the order of digits 135 = (1*10 2 ) + (3*10 1 ) + (5*10 0 ) In binary number (base 2) representation, only two digits 0 and 1 are used, in a similar way as decimal numbers = (1*2 4 )+(0*2 3 )+(0*2 2 )+(1*2 1 )+(1*2 0 ) = = = 19 = 19 Octal number: base 8 representation, using eight digits: 0, 1, 2, …, 7 Hexadecimal number: base 16 representation, using sixth digits: 0,1,2, 3, …, 9, A, B, C, D, E, F

4Module 5: CPU Conversion between binary and decimal = (1x2 0 )+(1x2 1 )+(0x2 2 )+(1x2 3 ) = = 11 Decimal to binary: repeatedly divide the quotient by 2, read the remainders backward = = Q R 11/ / / /2 0 1 Q R 19/ / / / /2 0 1

5Module 5: CPU One binary digit can represents two numbers, 0, 1 Two binary digits can represent four numbers 00, 01, 10, Three binary digits can represent ___numbers Fixed length binary representation

6Module 5: CPU Example of 4 binary digits numbers

7Module 5: CPU Binary number facts BitsRange 8 0 to = to = to = to = It takes more digits to represent a number in binary than it does in decimal

8Module 5: CPU Coding schemes Provide a common way of representing a character of data Common Schemes ASCII, 7 bits: ASCII, 7 bits: Unicode, 16 bits: Unicode, 16 bits: EBCDIC, 8 bits: EBCDIC, 8 bits:

9Module 5: CPU ASCII Stands for American Standard Code for Information Interchange Most widely used standard Used on virtually all personal computers

10Module 5: CPU ASCII coding scheme 7 bits, 127 different symbols Examples Dec BinarySymbols : (colon) : (colon) ; (semi-colon) ; (semi-colon) < (less than) < (less than) = (equal sign) = (equal sign) > (greater than) > (greater than) ? (question mark) ? (question mark) 064 (AT symbol) 064 (AT symbol) A A B B C C D D E E F F G G H H I I J J K K L L M M N N O O P P Q Q R R S S T T U U V V W W X X Y Y Z Z

11Module 5: CPU Unicode Designed to accommodate alphabets of more than 256 characters Uses 16 bits to represent one character 65,536 possible values 65,536 possible values Requires twice as much space to store data

12Module 5: CPU The unit of information Bit: short for binary digit Two possible values: 0 and 1 Two possible values: 0 and 1 Can never be empty Can never be empty Basic unit for storing data, information Basic unit for storing data, information Byte: a group of 8 bits Each byte has 256 (2 8 ) possible values Each byte has 256 (2 8 ) possible values For text, stores one character For text, stores one character Can be letter, digit, or special character Memory and storage devices measured in number of bytes Memory and storage devices measured in number of bytes

13Module 5: CPU Word The number of bits the CPU processes as a unit Typically a whole number of bytes Typically a whole number of bytes The larger the word, the more powerful the computer The larger the word, the more powerful the computer Personal computers typically 32 or 64 bits in length Personal computers typically 32 or 64 bits in length

14Module 5: CPU The units for information storage sizes One kilobyte (1 KB) = 1024 (2 10 ) bytes = 2 13 bits Memory capacity of older personal computers Memory capacity of older personal computers One Megabyte (1 MB) = 2 20 bytes ≈ 10 6 bytes (one million bytes) Personal computer memory Personal computer memory Portable storage devices (diskette, CD-ROM) Portable storage devices (diskette, CD-ROM) One gigabyte (1 GB) = 2 30 bytes ≈ 10 9 bytes (one billion bytes) Storage devices (hard drives) Storage devices (hard drives) Mainframe and network server memory Mainframe and network server memory One terabyte (1 TB) = 2 40 bytes ≈ bytes (one trillion bytes) Storage devices on very large systems Storage devices on very large systems

15Module 5: CPU Central Processing Unit (CPU) Consists of complex set of electronic circuitry Executes stored program instructions Three components Registers Registers Control unit Control unit Arithmetic/Logic Unit (ALU) Arithmetic/Logic Unit (ALU) Control Unit ALU Registers Memory CPU

16Module 5: CPU Registers Registers: temporary place for instructions and data. All instructions and data must be placed in registers before being executed and processed High-speed temporary storage areas Storage locations located within the CPU Storage locations located within the CPU Work under direction of control unit Accept, hold, and transfer instructions or data Accept, hold, and transfer instructions or data Keep track of where the next instruction to be executed or needed data is stored Keep track of where the next instruction to be executed or needed data is stored

17Module 5: CPU Control unit Control unit Control unit: directs the computer system to execute stored program instructions Must communicate with memory and ALU Storage operations Moving data/instructions from/to register to/from registers Moving data/instructions from/to register to/from registers Sends data and instructions from secondary storage to memory as needed Sends data and instructions from secondary storage to memory as needed

18Module 5: CPU ALU Executes all arithmetic and logical operations Arithmetic operations Arithmetic operations Addition, subtraction, multiplication, division Logical operations Logical operations Compare numbers, letters, or special characters Tests for one of three conditions Equal-to condition, Less-than condition, Greater-than condition Equal-to condition, Less-than condition, Greater-than condition Branch to different instructions Branch to different instructions

19Module 5: CPU Memory Also known as primary storage and main memory Often expressed as random-access memory (RAM) Often expressed as random-access memory (RAM) Not part of the CPU Not part of the CPU Holds data and instructions for processing Stores information only as long as the program is in operation

20Module 5: CPU The CPU and memory CPU cannot process data from disk or input device It must first reside in memory It must first reside in memory Control unit retrieves data from disk and moves it into memory Control unit retrieves data from disk and moves it into memory Items sent to ALU for processing Control unit sends items to ALU, then sends back to memory after processing Control unit sends items to ALU, then sends back to memory after processing Data and instructions held in memory until sent to an output or storage device or program is shut down

21Module 5: CPU Data storage and the CPU Two types of storage: Primary storage (memory) Primary storage (memory) Stores data temporarily CPU refers to it for both program instructions and data Secondary storage Secondary storage Long-term storage Stored on external medium, such as a disk