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

4
Chapter 2 Computer Hardware
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 its 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 its digital display
  once every minute to show the time
• An analog clock is continually moving its
  second, minute and hour hands to show the time

4
Chapter 2 Computer Hardware
4
Data Representation How do computers represent
data digitally?

• Another example is a 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
• Its rotating dial can be turned to many
  different positions to make the light varying
  degrees of bright or dim

4
Chapter 2 Computer Hardware
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 computers circuits have only two states on
  and off
• A binary 1 represents on
• A binary 0 represents off

4
Chapter 2 Computer Hardware
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

6
Chapter 2 Computer Hardware
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

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

8
Chapter 2 Computer Hardware
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

9
Chapter 2 Computer Hardware
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.

9
Chapter 2 Computer Hardware
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

10
Chapter 2 Computer Hardware
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)

11
Chapter 2 Computer Hardware
14
Self Quiz Questions

1. A(n) _______ device works with discrete numbers,
   whereas a(n) _______ device works with continuous
   data.
2. The _______ number system represents numeric data
   as a series of 0s and 1s.
3. Most personal computers use the _______ code to
   represent character data.
4. 100 Mb is larger than 100 MB. True or false?
5. A prefix that means a million bytes is _______.

11
Chapter 2 Computer Hardware
15
Self Quiz Answers

1. A(n) digital device works with discrete
   numbers, whereas a(n) analog device works with
   continuous data.
2. The binary number system represents numeric
   data as a series of 0s and 1s.
3. Most personal computers use the extended ASCII
   code to represent character data.
4. 100 Mb is larger than 100 MB. False
5. A prefix that means a million bytes is Mega .

11
Chapter 2 Computer Hardware