Download Mac: new

Introduction to Management Information Systems
Chapter 3 Computer Basics
HTM 304
Spring 06
Computer Basics
Hardware and Software Basics – group field study.
Digital Boolean Logics
Binary Number Systems
Computer Data
2
Introduction to Digital
We are in the digital age
Digital TV, Digital Phone, Digital Music Channel, …
What is digital?
“analog” – sine wave
Value -- Amplitude
many possible values
3
“Digital” – square wave
Value: -- High / Low voltage
two possible values
Benefit of using digital signal
Signal can be stored and processed more precisely
Easy to recover from small interference
Signal Weakens
During Transfer
Weaken, but still recoverable
Allow complicated computation task
4
Boolean Logics
Square wave only contain two signals:
High Voltage, representing Logic 1
Low Voltage, representing Logic 0
Logic 0
Logic 1
Electric Signals
0V
5V
Logics
False
True
Numeral Digits
0
1
All the complicated function a computer used is achieved via
digital circuits combined with basic logic gates
5
Logic Gates
Basic Logic Gate Products (e.g. TI 7645)
Example: a chip with four and gates
1
1
1
A variety chips and circuits composes a digital
circuit, achieving certain functionality, e.g. a
computer
6
Logic Functions (1)
And Function:
If both (all) inputs are True, then the output is True.
Example: If tomorrow is rainy AND you have to go to work, you
should prepare for an umbrella.
Rainy?
1– True, 0 – False
Work tomorrow?
1– True, 0 – False
Need an umbrella? 1– True, 0 – False
Formula:
0 and 0 = 0
0 and 1 = 0
1 and 0 = 0
1 and 1 = 1
Rule: 0 and anything is still 0, 1 and anything is anything.
7
Logic Functions (2)
Or Function:
If either (any) input is True, then the output is True.
Example: If I get a raise OR the bank gives me a loan, then I can
buy a new car.
Raise?
1– True, 0 – False
Loan?
1– True, 0 – False
New Car?
1– True, 0 – False
Formula:
0 or 0 = 0
0 or 1 = 1
1 or 0 = 1
1 or 1 = 1
Rule: 0 or anything is still anything, 1 or anything is 1.
8
Logic Functions (3)
Not Function:
If input is True, then the output is False.
Example: If your final score if below 60, you cannot pass.
<60?
pass?
1– True, 0 – False
1– True, 0 – False
Formula:
not 0 = 1
9
not 1 = 0
Exercise
Handout: Set 1 Logic Operations
10
Binary Number System
How computer computes with only 0-1s?
In decimal number system, there are 10 unique digits:
0, 1, 2, 3, 4, 5, 6, 7, 8, 9
In binary number system, there are only 2 unique digits:
0 and 1 
Base 10
(decimal)
Base 2
(binary)
0
1
2
3
4
5
6
7
0
1
?
?
?
?
?
?
Exercise: Handout Set 2.
11
Binary-to-Decimal Conversion (1)
Rule 1:
10...0
n 0 s
2
 2
n

10
Eg: 102=210, 1002=410, 1002=810
10,000,000,0002 = ?
Rule 2:
1...1 2   2n  1
n 1s
Eg: 112=22-1=310, 1112=23-1=710
1,111,111,1112 = ?
12
10
Binary-to-Decimal Conversion
Think what a decimal number really represent?
53710 = 5*100 + 3*10 + 7
= 5 * 102+ 3*101+7*100 -- base 10 system
8453310 = 8*104 +4*103 + 5*102 + 3*101+3*100
Binary System – base 2 system
10012 = 1*23+ 0*22 + 0*21+1*20 = 8 + 0 + 0 + 1 = 910
Use the following table to convert:
13
Binary
number
1
0
0
1
Place
Value
8
4
2
1
8
0
0
1
Sum up the last row
to get the decimal
number
910
Exercise
Handout Set 3
14
Decimal-to-Binary Conversion
How to represent 9810 using a binary number?
A short division method – divide the number by 2
2)
98
remainder
2) ________
49
0
24
2) ________
1
12
2) ________
0
6
2) ________
0
Read the remainders from below to
3
2) ________
0
above: 9810 = 11000102
1
2) ________
1
0
1
Continue until you get 0
15
Exercise
Convert the following decimal numbers to
binary numbers
127
96
231
37
51
255
16
Binary Addition
Basic Rules:
0+0=0
0+1=1
1 + 1 = 0 and a carry of 1
1 + 1 + 1 = 1 and a carry of 1
Examples
1001
+ 0011
1100
17
1110
+ 1000
10110
1010
+ 0111
10001
Exercises
Handout Set 4
18
Digital Signals in computer
How computer recognizes numbers physically?
19
Binary Numeral System
Computers represent data using binary
digits, called bits.
Bits are used for computer data because
they are easy to represent physically.
A switch can either be closed or open.
Computers use bits for two purpose:
Instruction and Data
For example:
a sequence 0111100010001110 means
adding two numbers together.
20
Computer Data
All computer data are represented by bits.
The data can be numbers, characters, currency
amounts, photos, recordings, or whatever.
Bits are grouped into 8-bit chunks called bytes.
The pros and cons of having fixed size bytes.
What is the largest value for a byte?
E.g. An IP address uses 4 bytes storage
21
Exercise:
Computer A is broadcasting its IP address 144.2.45.7 to
the network. How the electric signals are sent via the
network?
Binary Sequence
10010011 00000010 00101101 0000 0111
1 0 01 0 0 110 0 0 0 00 100 0 10 1 10 1 00 00 0 11 1
22
Using Bits to Represent Information
Use Character Representation Codes
ASCII - American Standard Code for Information Interchange
Check out the ASCII Table for digital sequence of the word “Hello”
Letters
Bytes
“H”
0100 1000
“e”
0110 0101
“l”
0110 1100
“l”
0110 1100
“o”
0110 1111
Each letter (“character”) is represented using 1 Byte = 8 bits
23
Important Storage-Capacity Terminology
24
Exercise:
1. Estimate the size of a text file with approximately 1000 characters
2. A 256 color bitmap graph uses one byte to store color information for
each pixel. Estimate the size of a bitmap file with 800*600 pixels
Ambiguity of Binary Data
A binary sequence 0100 0001 can be used to represent
both decimal value 65 and the character A
This ambiguity is more than curiosity; virus authors and
other cyber-criminal use it to their advantage.
Sometimes, bit-level encryption is used to insure secure
data storage and transmission over the net.
Binary Logic Operation is used
25
A simple example of encryption
E.g. Reverse the logic on the 1st and 3rd bits from the right
26
Letters
Bytes
Encrypted
Code
Encrypted
Letter
“H”
0100 1000
0100 1101
M
“e”
0110 0101
0110 0000
`
“l”
0110 1100
0110 1001
i
“l”
0110 1100
0110 1001
i
“o”
0110 1111
0110 1010
j
Exercise
Handout Set 5
27
Summary
Learning Binary to understand more about computer
Logic Operations: AND, OR, NOT
Count Binaries
Conversion: binary  decimal, decimal  binary
Binary addition
Use bytes to represent information
1 byte = ? bits
Check ASCII table for information
28
Field Study Assignment
Read the handout and Chapter 3
Find your group member
Prepare a presentation to address the questions in the
handout.
29