Lecture 1: 8/27/2002CS170 Fall CS170 Computer Organization and Architecture I Ayman Abdel-Hamid Department of Computer Science Old Dominion University Lecture 1: 8/27/2002

CS170 Fall Outline What is a computer? An overview of number systems Decimal Binary Octal Hexadecimal

Lecture 1: 8/27/2002CS170 Fall Processor Memory A Computer Input Output Five classic components of a computer: Input, Output, Memory, Data path, Control TapesKeyboardMousescanner DisplayPaper Processor

Lecture 1: 8/27/2002CS170 Fall Computers are built on two key principles All computers use the binary number system (base 2) (basic nature of electronic circuits ON/OFF, current flow/does not flow) Machine alphabet has two letters “0”, “1” Each letter is a binary digit “bit”. Byte is 8 bits Both instructions and data are represented by numbers Instructions and data are stored in memory and are read and written as numbers

Lecture 1: 8/27/2002CS170 Fall Number Systems Numbers can be represented in any base (humans use base 10) Symbols for a number system of base B are 0, 1, 2, …, B –1 decimal (base 10) 0, 1, 2,.., 9binary (base 2) 0, 1 notation “number B ” (375 in decimal is written , 1011 in binary is written ) Value of i th digit d is “d * B i” where i starts from 0 and increases from right to left 2 1 0ipositional notation 3 7 5d 5 * 10 0 =5 7 * 10 1 =70 3 * 10 2 =300 Three hundred and seventy five

Lecture 1: 8/27/2002CS170 Fall Conversion from binary to decimal Convert to decimal = (1 * 2 0 ) + (1 * 2 1 ) + (0 * 2 2 ) + (1 *2 3 ) = = i d This process can be used for conversion from any number system to decimal (TRY convert to decimal)

Lecture 1: 8/27/2002CS170 Fall Conversion from decimal to binary Convert to binary Step 1: divide value by 2 and record remainder Step 2: as long as quotient not zero, continue to divide the newest quotient by 2 and record the remainder Step 3: when obtain a zero as quotient, binary representation consists of remainders listed from right to left in order OperationQuotientremainder 13 by by by by =

Lecture 1: 8/27/2002CS170 Fall Conversion from decimal to binary Convert to octal (octal is base 8) Previous approach can be used to convert from decimal to any number system OperationQuotientremainder 13 by by = = (5 * 8 0 ) + (1 * 8 1 ) = 13 10

Lecture 1: 8/27/2002CS170 Fall Other Number Systems Octal (base 8) Symbols (0, 1, 2, 3, 4, 5, 6, 7) Working with too long binary numbers is a problem Hexadecimal (base 16) Symbols (0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F) Byte = 8 bits = 2 hex digits ( 1 hex digit is 4 bits)

Lecture 1: 8/27/2002CS170 Fall Conversion from binary to hex Convert to hex Divide binary number into 4 bits groups from right to left E 16 34E

Lecture 1: 8/27/2002CS170 Fall DecimalBinaryHexadecimal A B C D E F 2 0 = 12 7 = = 22 8 = = 42 9 = = = = = = = = = 8190 Kilo 2 10 Tera2 40 Mega 2 20 Peta2 50 Giga2 30