An Introduction to Computers August 12, 2008 Mrs. C. Furman

An Introduction to An Introduction to ComputersComputersAugust 12, 2008August 12, 2008

Mrs. C. FurmanMrs. C. Furman

4 Tasks of a Computer4 Tasks of a Computer

• Input Data – keyboard, mouse, scanner, microphone, digital camera, CD-RW/DVD drive, and disk drive.

• Store Data – integrated circuits.• Process Data – CPU, where decisions are

made. • Output Data – monitors, printers, CD-

RW’s, disk drives and memory keys store data and speakers.

CPUCPU

• Arithmetic Logic Unit, which can perform arithmetic and logic operations

• Executes instructions fast.

• Speed is determined by the computer’s clock rate.

• Clock Rate - measured in megahertz (MHz, million cycles per second) and gigahertz (GHz, billion cycles per second)

MemoryMemory

• ROM: Read Only Memory – most basic operations

• RAM: Random Access Memory – primary storage or main memory – data and instructions are temporarily stored

• RAM can be written to secondary storage.

• Secondary Storage – floppy disk, hard disk, memory key, or CD- RW.

ProgramsPrograms

• Application Software– Word, powerpoint, games…

• Operating System Software – OS – run automatically when the computer is turned on and is used to control processing and peripherals, run application software and control input and output. – Windows, Mac OS X Tiger, Unix, and Linux

Programming LanguagesProgramming Languages

• A set of words, codes and symbols that allow a programmer to give instructions to the computer.

• Low – level and High – level programs…

Low – Level LanguagesLow – Level Languages

• Machine language – first generation language.– Consists of 0’s and 1’s

• Assembly language– Same instructions and structures as machine

language– Uses meaningful names or abbreviations

instead of numbers.– Second generation language.

High-Level LanguagesHigh-Level Languages

• Third generation languages• Developed in late 1950s• English-like instructions • Easier to use than machine language• Fortran, Pascal, C, C++, Java• Compilers – program that convert high-level

language into machine language. • Interpreter – also translates the program but

does it line by line, executing as they go.

How is Data Stored?How is Data Stored?

Data – computer representation of something in the real world.

Circuits – 2 states ON /OFFImagine 2 light bulbs / 2 switches, what are

the possible combinations?

OFF / OFF

OFF / ON

ON / OFF

ON / ON

What about 3 lights? How What about 3 lights? How many combinations?many combinations?

What about 8 lights?What about 8 lights?

Apply to the computer…Apply to the computer…• Use a special number system: Binary

number system.

• Decimal Number System: base 10 , digits 0 – 9. (Our number system)

• Binary Number System: base 2, digits 0 and 1. 0 represents off (false), 1 represents on (true).

• A single binary digit is called a bit.

Converting Binary to DecimalConverting Binary to Decimal

Decimal Numbers:

7403 = 7 x1000 + 4x100+ 0x10 + 3 x 1

3x100 = 3

0x101 = 0

4x102 = 400

7x103 = 7000

7403

Same process as previous slide, but base 28 bits in 1 byte:1011 0110

0x20 = 01x21 = 21x22 = 40x23 = 01x24 = 161x25 = 320x26 = 01x27 = 128

Binary to DecimalBinary to Decimal

Total: 182

8 bits = 1 byte

What’s the number of combinations in 1 byte?

What numbers can be represented with 1 byte?

ExamplesExamples

a. 1111 0000

b. 1010 1010

c. 1100 1100

d. 0011 0011

Converting Decimal to BinaryConverting Decimal to Binary

Binary Is base 2

We multiply to go from binary to decimal.

We divide to go from decimal to binary.

Right most digit tells even or odd. 1 – even 0 – odd.

Convert Decimal to BinaryConvert Decimal to Binary

a. Convert 210 to binary.

b. 151

HexadecimalHexadecimal

• Hexadecimal: Used to represent 4 binary digits.

1111 = 15 and 0000 = 0, so it is base 16.

Digits 0 – 9 plus A – F

A:10, B:11, C:12, D:13, E:14, F:15

Hexadecimal to decimalHexadecimal to decimal

1f

15x160 = 15

1x161 = 16

31

Change from Hexadecimal to Change from Hexadecimal to Binary and DecimalBinary and Decimal

0

A

19

1E

OctalOctal• Octal is base 8 – digits 0 - 7• Convert 10478 to decimal

1047 7x80 = 7

4x81 = 32 0x82 = 0 1x83 = 512

= 551

What is the decimal equivalent?What is the decimal equivalent?

1112 3458

2C16