CSCI 125 & 161

Lecture 2

Martin van Bommel

Hardware vs Software

• Hardware - physical components you can see and touch– e.g. processor, keyboard, disk drive

• Software - instructions for hardware– e.g. operating system, compiler, word processor

Software Development

• Early computers - complex coding schemes– machine language - 0’s and 1’s

• Later on - introduction of system software– assembly language - mnemonics for operations– assembly program assembler machine lang

• Even later - compilers created– high-level languages (HLL) - natural language– HLL program compiler machine language

High Level Languages• 1957 - John Backus - FORTRAN• 1958, 60, 64 - ALGOL, COBOL, BASIC • 1970 - US Dept. of Defence - Ada• 1971 - Nicklaus Wirth - Pascal• 1972 - Dennis Ritchie - C• 1977 - Nicklaus Wirth - Modula-2• 1983 – Bjarne Stroustrup – C++ (C with class)• 1989 - ANSI C adopted• 1998 – ANSI C++ adopted

Computer Components

• CPU - Central Processing Unit– controls operation of entire systems– performs arithmetic and logic operations– stores and retrieves instructions and data

contains

• ALU - Arithmetic-Logic Unit

• Control Unit

Components (con’t)

• Main memory (internal or primary memory)– RAM - Random Access Memory– stores instructions and data temporarily

• Secondary memory (external or auxiliary)– magnetic disk (hard disk or floppy), tape– CD-ROM, DVD-ROM, Flash drive, etc.

• Peripherals - used for Input/Output– keyboard, printer, monitor, etc.

Internal Representation

• Each unit of memory a two-state device– off or on, 0 or 1– represent in Binary, two Binary Digits (bits)

• Organized into groups of 8 bits - bytes– represents single keyboard character

• Larger grouping of 16 or 32 bits - word– represents single integer value– identified by address for access

Memory Sizes

• Kilobyte (K) = 210 = 1,024 bytes

• Megabyte (Mb) = 220 = 1,048,576 bytes

• Gigabyte (Gb) = 230 = 1,073,741,824 bytes

SI Memory Sizes• System International – Convention

• Kilobyte = 103 bytes = one thousand bytes• Megabyte = 106 bytes = one million bytes• Gigabyte = 109 bytes = one billion bytes

• Kibibyte (K) = 210 = 1,024 bytes• Mebibyte (Mb) = 220 = 1,048,576 bytes• Gibibyte (Gb) = 230 = 1,073,741,824 bytes

Decimal Number Systems• Base 10

• Digits - 0, 1, 2, 3, 4, 5, 6, 7, 8, 9

• e.g. 34210 =

= 3 x 102 + 4 x 101 + 2 x100

= 3 x 100 + 4 x 10 + 2 x 1

= 300 + 40 + 2

Binary Number System

• Base 2

• Digits 0, 1

• e.g. 1102 =

= 1 x 22 + 1 x 21 + 0 x 20

= 1 x 4 + 1 x 2 + 0 x 1

= 4 + 2 + 0

= 6

Counting in Binary

DecimalBinary

0 0

1 1

2 10

3 11

4 100

5 101

DecimalBinary

6 110

7 111

8 1000

9 1001

10 1010

11 1011

Character Representation

• 1 byte = 8 bits = 1 character?

• 256 possible codes with 8 bits

• Assign a character to each code

• Common assignment– ASCII - American Standard Code for

Information Interchange – defines first 128

ASCII CodeCode Value Letter

0 Null character

1 - 31 Special Control Characters

10 \n = New line

32 Space

33-47, 58-64, 91-96 Punctuation

48 - 57 0 - 9

65 - 90 A - Z

97 - 122 a - z

Interesting ASCII Choice?

• Digits 0 through 9 seem strange?

Digit Dec Hex

0 48 30 1 49 31

… … …

9 57 39

Unicode

• International language coding standard

• Superset of ASCII

• Various codes defined to use upper 128 bits for symbols and other languages

16 bits?

• Two characters?

• One integer?

• Part of a floating point?

• Machine language instruction?

• Memory address?

• Depends on application!