1. Comp 1001
Introduction to Information Technology & Computer Architecture
Wednesday 12-1Dr. Joe Carthy

2. Comp 1001: IT & Architecture - Joe Carthy
Course Outline
Introduction to Information Technology
Hardware and Software
I/O and Storage devices
CPU
RAM
Information Representation:
ASCII codes
Binary and Hexadecimal Numbers
Computer Networks
Operating Systems
Comp 1001: IT & Architecture - Joe Carthy

3. Course Outline Continued
Computer Architecture and Assembly Language
CPU structure
Introduction to Assembly Language (8086)
Instruction Set
Basic Assembly Language Programs
Fetch-Execute Cycle
Pipelining
Memory: RAM access and Cache Memory
Computer performance evaluation
Practicals
Comp 1001: IT & Architecture - Joe Carthy

4. Course Outcomes At the end of this course
Students should have a grasp of
functional components of a computer system
information representation
assembly language instructions
instruction execution
CPU structure and functioning
knowledge of performance evaluation
Comp 1001: IT & Architecture - Joe Carthy

5. Comp 1001: IT & Architecture - Joe Carthy
Recommended Texts
Recommended Texts:
Computers (Tools for the Information Age), Brief Edition, H.L. Capron, Prentice Hall
Introduction to Assembly Language Programming and Computer Architecture, J. Carthy, ITP
Web Notes
Comp 1001: IT & Architecture - Joe Carthy

6. Simple Model of a Computer System
Hardware
Physical components that make up a computer system
System: interconnected set of devices that function as a unit
Software
Computer programs that allow you use a computer
Comp 1001: IT & Architecture - Joe Carthy

7. Simple Model of a Computer System Version 1
Comp 1001: IT & Architecture - Joe Carthy

8. Simple Model of a Computer System Version 2
Comp 1001: IT & Architecture - Joe Carthy

9. Comp 1001: IT & Architecture - Joe Carthy
System Devices
Classified as:
Storage devices: store information
RAM
Disk
CD/DVD
Input/Output (I/O) devices: carry info to/from Computer
Monitor (screen)
Printer
Mouse/Keyboard
Speakers
Comp 1001: IT & Architecture - Joe Carthy

10. Comp 1001: IT & Architecture - Joe Carthy
Review Questions
What is a computer system ?
Explain the difference between hardware and software
What are the two major device classes ?
What is a peripheral device ?
What is the function of the processor ?
What is the function of memory (RAM) ?
What are the major devices ?
What is a bus ?
Comp 1001: IT & Architecture - Joe Carthy

11. Information Representation
How is “information” represented in a computer system ?
What are the different types of information
Text
Numbers
Images
Video
Photographic
Audio
Comp 1001: IT & Architecture - Joe Carthy

12. Everything is in Binary ! (1’s and 0’s)
Computers are digital devices - they can only manipulate information in digital (binary) form.
Easy to represent 1 and 0 in electronic, magnetic and optical devices
Only need two states
High/low
On/off
Up/down
etc
All information in a computer system is
Processed in binary form
Stored in binary form
Transmitted in binary form
Comp 1001: IT & Architecture - Joe Carthy

13. How is information converted to Binary form
I/O and Storage Devices are digital
I/O devices convert information to/from binary
A keyboard converts the character “A” you type into a binary code to represent “A”
E.g. “A” is represented by the binary code
Monitor converts to the “A” that you read
Comp 1001: IT & Architecture - Joe Carthy

14. Comp 1001: IT & Architecture - Joe Carthy
Bits and Bytes
One binary digit i.e. 1 or 0 is called a bit
A group of 8 bits is one byte
Byte is the unit of storage measurement
Number of Bytes
Unit
1024 bytes (210 bytes)
1 Kilobyte (Kb)
1024 Kb (220 bytes)
1 Megabyte (Mb)
1024 Mb (230 bytes)
1 Gigabyte (Gb)
1024 Gb (240 bytes)
1 Terabyte (Tb)
1024 Tb (250 bytes)
1 Petabyte (Pb)
Comp 1001: IT & Architecture - Joe Carthy

15. Representing Text- ASCII Code
Textual information is made up of individual characters e.g.
Letters:
Lowercase: a,b,c,..z
Uppercase: A,B,C..Z
Digits: 0,1,2,..9
Punctuation characters: ., :, ; ,, “, ’
Other symbols: -, +, &, %, #, /,\,£, etc.).
Comp 1001: IT & Architecture - Joe Carthy

16. Representing Text- ASCII Code
Each character is represented by a unique binary code.
ASCII is one international standard that specifies the binary code for each character.
American Standard Code for Information Interchange
It is a 7-bit code - every character is represented by 7 bits
There are other standards such as EBCDIC but these are not widely used.
ASCII is being superceded by Unicode of which ASCII is a subset. Unicode is a 16-bit code.
Comp 1001: IT & Architecture - Joe Carthy

17. Comp 1001: IT & Architecture - Joe Carthy
Sample ASCII Codes
Char
ASCII
Decimal
NUL 00
BEL 07 LF 10 CR 13 48 SP 20 1 49 ! 21 2 50 “ 22 9 57 A 65 a 97 B 66 b 98 C 67 c 99 Y 89 y
121 Z 90 z
122
Comp 1001: IT & Architecture - Joe Carthy

18. Comments on ASCII Codes
Codes for A to Z and a to z form collating sequences
A is 65, B is 66, C is 67 and so on
A is 97, b is 98, c is 99 and so on
Lowercase code is 32 greater than Uppercase equivalent
Note that digit ‘0’ is not the same as number 0
ASCII is used for characters
Not used to represent numbers (See later)
Codes 0 to 30 are typically for Control Characters
Bel - causes speaker to beep !
Carriage Return (CR); LineFeed (LF)
Others used to control communication between devices
SYN, ACK, NAK, DLE etc
Comp 1001: IT & Architecture - Joe Carthy

19. Comp 1001: IT & Architecture - Joe Carthy
Review
All information stored/transmitted in binary
Devices convert to/from binary to other forms that humans understand
Bits and Bytes
Kb, Mb, Gb, Tb and Pb are storage metrics
ASCII code is a 7-bit code to represent text characters
Text “numbers” not the same as “maths” numbers
Do not add phone numbers or get average of PPS numbers !
Comp 1001: IT & Architecture - Joe Carthy

20. Comp 1001: IT & Architecture - Joe Carthy
Review Questions
How is information transmitted inside a computer
Why do we use binary in computers
What is an ASCII code used for
How big is an ASCII code
What is the ASCII code for: A, ‘0’, ‘a’
What is a collating sequence
What is a control character - give an example
What is Unicode and why is it used
What is a bit ? A byte ?
How many bytes in: Kb, Mb, Gb, Tb, Pb
Comp 1001: IT & Architecture - Joe Carthy

21. Representing Numbers: Integers
Humans use Decimal Number System
Computers use Binary Number System
Important to understand Decimal system before looking at binary system
Decimal Numbers - Base 10
10 digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9
Positional number system: the position of a digit in a number determines its value
Take the number 1649
The 1 is worth 1000
The 9 is worth 9 units
Formally, the digits in a decimal number are weighted by increasing powers of 10 i.e. they use the base 10. We can write 1649 in the following form:
1* * * *100
Comp 1001: IT & Architecture - Joe Carthy

22. Representing Numbers: Integers
weighting:
Digits
1649 = 1* * * *100
Least Significant Digit: rightmost one - 9 above
Lowest power of 10 weighting
Digits on the right hand side are called the low-order digits (lower powers of 10).
Most Significant Digit: leftmost one - 1 above
Highest power of 10 weighting
The digits on the left hand side are called the high-order digits (higher powers of 10)
Comp 1001: IT & Architecture - Joe Carthy

23. Representing Numbers: Decimal Numbers
Largest n-digit number ?
Made up of n consecutive 9’s (= 10n -1 )
Largest 4-digit number if 9999
9999 is
Distinguishing Decimal from other number systems such as Binary, Hexadecimal (base 16) and Octal (base 8)
How do we know whether the number 111 is decimal or binary
One convention is to use subscripts
Decimal: Binary:1112 Hex: Octal: 1118
Difficult to write use keyboard
Another convention is to append a letter (D, B, H, O)
Decimal: 111D Binary:111B Hex: 111H Octal: 111O
Comp 1001: IT & Architecture - Joe Carthy

24. Representing Numbers: Binary Numbers
Binary numbers are Base 2 numbers
Only 2 digits: 0 and 1
Formally, the digits in a binary number are weighted by increasing powers of 2
They operate as decimal numbers do in all other respects
Consider the binary number
Weight
bits
= 0*27 + 1*26 + 0*25 + 1*24 + 1*23 + 1*22 + 0*21 + 0*20 =
= 9210
Comp 1001: IT & Architecture - Joe Carthy

25. Representing Numbers: Binary Numbers
Leftmost bit is the most significant bit (MSB).
The leftmost bits in a binary number are referred to as the high-order bits.
Rightmost bit is the least significant bit (LSB).
The rightmost bits in a binary number are referred to as the low-order bits.
Largest n-bit binary number ?
Made up of n consecutive 1’s (= 2n -1)
e.g. largest 4-bit number: 1111 = = 15
Comp 1001: IT & Architecture - Joe Carthy

26. Representing Numbers: Binary Numbers
Exercises
Convert the following binary numbers to decimal:
(i) (ii) (iii)
(iv) (v) (vi)
Joe Carthy Formatting Convention
In these notes we insert a space after every 4 bits to make the numbers easier to read
Comp 1001: IT & Architecture - Joe Carthy

27. Representing Numbers: Converting Decimal to Binary
To convert from one number base to another:
you repeatedly divide the number to be converted by the new base
the remainder of the division at each stage becomes a digit in the new base
until the result of the division is 0.
Example: To convert decimal 35 to binary we do the following:
Remainder
35 / 2 1
17 / 2 1
8 / 2 0
4 / 2 0
2 / 2 0
1 / 2 1
The result is read upwards giving 3510 =
Comp 1001: IT & Architecture - Joe Carthy

28. Representing Numbers: Converting Decimal to Binary
Exercise: Convert the following decimal numbers to binary
(1) 64 (2) 65 (3) 32 (4) 16 (5) 48
Shortcuts
To convert any decimal number which is a power of 2, to binary, simply write 1 followed by the number of zeros given by the power of 2.
For example, 32 is 25, so we write it as 1 followed by 5 zeros, i.e ; 128 is 27 so we write it as 1 followed by 7 zeros, i.e
Remember that the largest binary number that can be stored in a given number of bits is made up of n 1’s.
An easy way to convert this to decimal, is to note that this is 2n - 1.
For example, if we are using 4-bit numbers, the largest value we can represent is 1111 which is 24-1, i.e. 15
Comp 1001: IT & Architecture - Joe Carthy

29. Representing Numbers: Converting Decimal to Binary
Binary Numbers that you should remember because they occur so frequently
Binary
Decimal
111 7
1111 15
127
255
Comp 1001: IT & Architecture - Joe Carthy

30. Comp 1001: IT & Architecture - Joe Carthy
Review
Decimal Number System - Base 10
Significant Digits
Binary Number System - Base 2
Notation (B,D,H,O)
Binary to Decimal
Decimal to Binary
Shortcuts and Common Binary Numbers
Review Questions
What is a positional number system ?
What is the MSB and the LSB. Give an example of each one.
Show how the weights of the bits in an
8-bit binary number
16-bit binary numbe
What is the weight of the MSB in (a) 8-bit number (b) 16-bit number (c) 32-bit number
Convert 48D, 65D, 31D, 15D to binary
Convert B, B and B to decimal
Comp 1001: IT & Architecture - Joe Carthy