Chapter 2 Computer Hardware

1. Chapter 2Computer Hardware Section A: Data Representation and Digital Electronics Computer Concepts 7th EditionParsons/Oja

2. Data Representation: How do computers represent data digitally? • Data is defined as the symbols that represent things, people, events and ideas • Computers store data in digital format as a series of 1s and 0s (known as binary code) • Each 1 and 0 is called a bit • Eight bits is called a byte • The term bit comes from “binary digit” • Bytes are used to represent one character – a letter, number, or punctuation mark • For example, the letter H is represented in binary code as 01001000 • An exclamation point (!) is 001000001 Chapter 2: Computer Hardware 4

3. Data Representation: How do computers represent data digitally? • Digital data is made up of discrete numbers, with each bit being either a 1 or a 0 – it’s either on or off, nowhere in between • Analog data is made up of a continuous wave of information, with varying degrees in between • For example: • A digital clock changes it’s digital display once every minute to show the time • An analog clock is continually moving it’s second, minute and hour hands to show the time Chapter 2: Computer Hardware 4

4. Data Representation: How do computers represent data digitally? • Another example isa light fixture • A standard light switch is similar to digital • It is either on or off – 1 or 0 • A dimmer light switch is similar to analog • It’s rotating dial can be turned to many different positions to make the light varying degrees of bright or dim Chapter 2: Computer Hardware 4

5. Data Representation: How do computers represent data digitally? • Data representation makes it possible to convert letters, sounds, and images into electrical signals • Digital electronics makes it possible for computer to manipulate simple “on” and “off” signals to perform complex tasks • A computer’s circuits have only two states: on and off • A binary 1 represents “on” • A binary 0 represents “off” Chapter 2: Computer Hardware 4

6. How can a computer represent numbers? • Unlike the decimal system (base 10), the binary number system (base 2) uses only two digits: 0 and 1 • The following table lists some decimal numbers and their binary equivalent: Chapter 2: Computer Hardware 6

7. How can a computer represent words and letters using bits? • Character data is composed of letters, symbols, and numbers that will not be used in arithmetic operations • Numeric data is used in arithmetic calculations, and is encoded differently • ASCII (American Standard Code for Information Interchange) requires only 7 bits for each character • Extended ASCII uses 8 bits for each character. Used in most personal computers • See the code on the next slide Chapter 2: Computer Hardware 7

8. How can a computer represent words and letters using bits? Chapter 2: Computer Hardware 7

9. How can a computer represent words and letters using bits? • EBCDIC (Extended Binary-Coded Decimal Interchange Code) is an alternative 8-bit used by older IBM systems • Unicode uses 16 bits and provides codes for 65,000 characters – a bonus for representing alphabets of multiple languages • Used for foreign language support Chapter 2: Computer Hardware 8

10. How does a computer convert sounds and pictures into codes? • Sounds and pictures must be transformed into a format the computer can understand • A computer must digitize colors, notes, and instrument sounds into 1s and 0s • For example, a red dot on your screen might be represented by 1100, a green dot by 1101 Chapter 2: Computer Hardware 9

11. How does a computer store all these codes? • Data is stored on a computer in a file • Data files might contain the text of a document, the numbers for a calculation, the contents of a web page, or the notes of a music clip as binary code • Executable files contain the programs or instructions that tell the computer how to perform a specific task. For example, how to display and print text • Data files have a file header which tells the computer how the binary code is used to represent the data. • The header tells the computer if the binary code represents a music file, a graphic, a text document, etc. Chapter 2: Computer Hardware 9

12. Quantifying Bits and bytes: How can I tell the difference between bits and bytes? • A bit is one binary digit (b) • Eg. 0 • A byte is 8 bits (B) • Eg. 0010 0100 • A nibble is 4 bits • Eg. 0011 Chapter 2: Computer Hardware 10

13. Quantifying Bits and bytes: How can I tell the difference between bits and bytes? • Prefixes • Kilo- means a 1000 • Mega- means million • Giga- means billion • Kilobit (Kb) is approx. 1,000 bits (1,024) • Kilobyte (KB) is approx. 1,000 bytes (1,024) • Megabyte (MB) is approx. 1,000,000 bytes (1,048,576) • Gigabyte (GB) is approx. 1,000,000,000 bytes (1,073,741,824) Chapter 2: Computer Hardware 11

14. Self Quiz Questions • A(n) _______ device works with discrete numbers, whereas a(n) _______ device works with continuous data. • The _______ number system represents numeric data as a series of 0s and 1s. • Most personal computers use the _______ code to represent character data. • 100 Mb is larger than 100 MB. True or false? • A prefix that means a million bytes is _______. Chapter 2: Computer Hardware 11

15. Self Quiz Answers • A(n) digital device works with discrete numbers, whereas a(n) analog device works with continuous data. • The binary number system represents numeric data as a series of 0s and 1s. • Most personal computers use the extended ASCII code to represent character data. • 100 Mb is larger than 100 MB. False • A prefix that means a million bytes is Mega . Chapter 2: Computer Hardware 11