1. Introduction to Computer Systems and Software
Lecture 1 of 2
Simon Coupland

2. Contents Technology and Computer Evolution
Introduction to Computer Systems
Computer Hardware
Computer Software

3. Computer System Users Types of User: End-user Applications Programmer
Low-level Programmer and Hardware Designer

4. The End User The vast majority of computer users are end users
View computers as tools – black boxes
Use a set of application programs to achieve a specific goal or to solve a specific problem:
Word processor
Spreadsheet
CAD (Computer Aided Design)
DTP (Desktop Publishing)

5. The End User
Purchase is based upon complete set of hardware and software according to application environment,
No need to have knowledge of design, implementation and testing at hardware and software level.

6. Applications Programmers
People who provide what end users want
Computer Scientists or Engineers.
Little knowledge of hardware
Appreciation for business logic
Technically and generally mathematically literate

7. Low-Level Programmers and Hardware Designers
Electronic engineers
Computer scientists
Knowledge of machine architecture (Why?)
Knowledge of electronics
Real-time, bit manipulation and hardware resources
Program in assembler and C
Hardware design in FPGA, VHDL and more rarely ASIC

8. Low-Level Programmers and Hardware Designers
Advantage of using Assembly Language:
Used in industrial time critical applications
In-depth understanding;
Instructions (arithmetic, Logical and I/O)
Instruction phases (fetch, decode and execute)
Information representation (pointers, data)
understanding of processor architecture.
Difference between pointers and data?

9. Machine Code Very simple low level instructions.
A single high level language instruction (e.g. VB) may require many machine code instructions.
An integral part of the processor.
An instruction has an operation code (opcode), followed by zero or more items of data (operands)
© De Montfort University, 2007
CSCI1412-HW-3

10. A Microcomputer System
Three components:
Hardware
Software
Data

11. Hardware The physical equipment:
Base unit – printed circuit boards (processor, memory and I/O), power supply and connections
Interface – VDU/monitor, keyboard and mouse
Peripherals – Disks, CD/DVD, printers and scanners

12. Hardware CPU Components Traditionally the CPU also included
CU: Control Unit
interprets stored instructions in sequence
issues commands to all elements of the computer system
ALU: Arithmetic & Logic Unit
performs arithmetic and logic instructions
Traditionally the CPU also included
RAM: Random Access Memory
holds data, instructions and results of processing
temporary (volatile)

13. Hardware Often, CPU is used to mean just the CU and ALU
the ‘processor’ or ‘microprocessor’ other physical equipment:
Base unit – printed circuit boards (processor, memory and I/O), power supply and connections
Interface – VDU/monitor, keyboard and mouse
Peripherals – Disks, CD/DVD, printers and scanners

14. Hardware
notice that all information enters and leaves the CPU via the RAM
CPU
Input
Devices
Communication
Backing Storage
Output
control
unit
arithmetic & logic unit
RAM
(micro-)
processor
Why CU and ALU are two separate entities?

15. Software A sequence of instructions that tell the computer what to do
Controls the hardware
Processes inputs and gives outputs
Examples: linux, windows, internet explorer, gcc, etc

16. Data Inputs files Settings – registry, .ini files, .conf files
Some cross over - batch files and shell scripts

17. Terminology Byte a group of 8 bits Word Bit (binary digit, ‘0’ or ‘1’)
easy to represent as magnetic fields, light/electrical pulses, etc.
Byte a group of 8 bits
nibble = 4 bits (a small byte!)
Word
a group of bits that can be manipulated by the processor as a single unit
almost always it is a whole number of 8-bit bytes

18. Terminology memory capacities are currently in billions of bytes
disk capacities are in billions or trillions of bytes
Representation?
Kb = Kilobyte = 1024 bytes = 1024  8 bits = 210
Mb = Megabyte = 1024 Kb = (1024)2 bytes = 220
Gb = Gigabyte = 1024 Mb = (1024)3 bytes = 230
Tb = Terabyte = 1024 Gb = (1024)4 bytes = 240
Pb = Petabyte = 1024 Tb = (1024)5 bytes = 250

19. Instruction and Data Storage
Number representation
Fundamental to all computer system is the notion of a binary digit - 0 or 1 – called a bit.
Decimal System (base 10)
Binary System (base 2)
Hexadecimal System (base 16)
Octal System (base 8)

20. Instruction and Data Storage
Integers (a number with no decimal points)
An unsigned byte – range 0 to 255
bit 7 6 5 4 3 2 1
value 27 26 24 23 22 21 20
128 64 32 16 8
= = 77
= = 187

21. Instruction and Data Storage
Negative Integers
An twos compliment signed byte – range -128 to +127
Most significant bit stores the sign (1 for -, 0 for +)
When negative, result = result
bit 7 6 5 4 3 2 1
value
-/+ 26 24 23 22 21 20
-128/+ 64 32 16 8
= = 77
= = -51

22. Instruction and Data Storage
Hexadecimal 8 = 9
uses powers of 16:
160 = 1
161 = 16
162 = 256
163 = 4,096
164 = 65,536
165 = 1,048,576 = 1 2 3 4 5 6 7 A = 10 B 11 C 12 D 13 E 14 F 15

23. Instruction and Data Storage
Real numbers
Floating point binary representations are used to represent real numbers (a number that has a decimal point)
It is possible to use fixed point binary representation, generally not used because of inflexibility

24. Instruction and Data Storage
Real numbers
,  108,  10-34
A number is split into two parts
one part describes the number itself (the mantissa)
another describes where the decimal point appears (the exponent)

25. Characters (text) Text is a collection (an array) of characters
Generally characters are encoded in ASCII (American Standard Code for Information Interchange)
Example: “Hi!”
Character H i !
ASCII value 72
105 33
Binary

26. Low Level Computer Languages
Assembly language
Direct interaction with all parts of the hardware
Specific to each microprocessor
Great for real-time execution
Nearly impossible to code large tasks

27. Low Level Computer Languages
Assembly language
Example on MC series
CLR.W D3
Clear the lower 16 bit the data register D3

28. High Level Computer Languages
Higher level of abstract from the hardware
Less direct interaction with the hardware
Example languages:
C (can be low level)
C++
Java
BASIC
FORTRAN
COBOL

29. High Level Computer Languages
Example in C
int D0 = * (267 – 23);
Equivalent in MC assembler
MOVE.L #267,D0
SUB.W #23,D0
ADD.W D0,D0
ADD.W #7,D0

30. Technology and Computer Evolution

31. Computer Generations
Computer systems are large collections of electronic switches
The power of a computer depends on the number of these electronic ‘binary’ switches

32. Computer Generations First Generation (1940’s)
Switches were thermionic valves
Heated cathode produces negatively charged electrons
Flow of electrons to positive anode controlled by charged grid
Very large
Prone to breakdowns

33. Computer Generations
Thermionic valve / vacuum tube

34. Computer Generations Second Generation (1950’s)
Switches were transistors
The flow of electrons between an ‘emitter’ and a ‘collector’ is controlled by the current supplied to a ‘base’ semi conducting material
5mm in height
Don’t breakdown

35. Computer Generations
The Transistor
Collector
Emitter
Base

36. Computer Generations Third Generation (1960’s)
Switches were fabricated into small scale integrated circuits (IC’s)
Still use semiconductors
Many transistors built onto a single chip
Much smaller
More processing power

37. Computer Generations Forth Generation (1970’s to date)
Miniaturization is the key
Small scale integration transistors
Medium scale integration transistors
Large scale integration transistors
Very large scale integration 64K – 200K transistors
Ultra large scale integration 200K – 100M + transistors

38. Computer Generations Moore’s Law Gordon Moore – co-founder of Intel
Transistor density on IC’s will double every eighteen months

39. Computer Generations

40. Computer Generations Moore’s Law – the limit
Research suggests that the smallest possible transistor will be 16-nanometres
Expected to be reached around 2020
Then what?
Quantum computing
Bio computing
Unknown alternative to the transistor

41. Computer Hardware

42. Computer Hardware

43. Computer Hardware Components: CPU (Central Processing Unit)
Co-Processor (floating-point math, graphics)
Primary memory (RAM and ROM)
Disk controller
Input/Output devices and peripherals

44. Computer Hardware Buses:
Address bus – carries address of memory being accessed
Data bus – carries the data
Control bus – carries control signals between CPU and other components

45. Buses
Computer memory is made up of a set of locations. Each has a unique address.
 The address bus specifies the location. The data bus transfers the data.
The control bus determines e.g. read or write

46. The System Clock What controls the fetch / execute cycle?
this is a quartz chip that provides pulses at a regular, rapid, rate, like a metronome
n.b. not the same as the real date / time clock
The first microprocessor originally ran at 100 KHz, the Pentium IV is now at 1.2 – 4.0 GHz
A clock tick starts the fetch / execute cycle
it may take several (perhaps tens of) clock ticks to complete one complex instruction
© De Montfort University, 2007
CSCI1412-HW-3

47. Gigahertz
The ‘simplest’ measure of speed is just the rate at which the system clock ticks
usually quoted in Gigahertz (GHz)
1 Hertz = 1 cycle per second
1 Megahertz = 1 million cycles per second
1 Gigahertz = 1 billion cycles per second
This is meaningful in one type of processor
e.g. 2.4 GHz Pentium is twice as quick as 1.2 GHz
But is not for comparing different processor types
different processors may take different numbers of cycles to fetch / execute the ‘same’ instruction
e.g. a Pentium takes X cycles to load a number into the accumulator, whereas a takes Y cycles
© De Montfort University, 2007
CSCI1412-HW-3

48. Computer Hardware Memory:
Registers – store temporary data within the processor
Cache – stores temporary data that is likely to be used with the processor
Primary memory – RAM, stores programs being executed
Secondary memory – Disks, persistent storage

49. Computer Hardware
Memory:
Organised as a table: 1 2 3 4 5 6 7 8 9

50. Computer Hardware Inside the CPU ALU Control unit Clock Pipeline Data
Instruction
Internal cache memory
RAM
External cache memory
Data
Address
Control

51. Computer Hardware Inside the CPU – The Control Unit
In overall control of the computer system
Controls the fetch/execute cycle
Registers:
Program counter – hold the memory address of the next word in the current instruction
Instruction register – holds the next instruction to be executed

52. Computer Hardware Inside the CPU – Fetch/Excute Fetch Execute
Fetch the instruction from memory. Decode it and it the instruction has a indirect memory address find out the effective address in memory.
Execute
Execute the instruction by send the series of signals from the control unit to the ALU. Store the result or send it to an output device.

53. The Fetch / Execute Cycle
control unit
arithmetic /
logic unit
decode
execute
fetch
(store)
RAM

54. Computer Hardware Inside the CPU – the Arithmetic/Logic Unit
Integer arithmetic – addition, subtraction, multiplication and division
Logical operations – not, and, or, exclusive or and Bit shift operations
Data, address and status registers

55. Computer Hardware Co-Processors
Mathematical – to perform high speed floating point number calculations
Graphical – to produce video output from computer models. Modern graphics co-processors often implement an API (DirectX, OpenGL) in hardware

56. Computer Software

57. Computer Software System start-up
Uses firmware (software stored in ROM) generally called the BIOS, Basic Input/Output System
Initialises hardware
Performs Power On Self Test
Starts the operating system

58. Computer Software Operating System – OS Controls hardware and software
Windows, Linux, MAC OS X
Provides the initial front end experience to the end user
Does all the backroom work to keep things running smoothly

59. Computer Software Assemblers, Compilers and Interpreters
Assemblers convert assembly language into machine code
Compilers convert text written a programming language into machine code.
Cross assemblers/compilers convert code into machine code for a different machine
Interpreters execute programming code on line at a time

60. Computer Software Java – the Exception
Originally called Oak, java was intended to be the de facto language for embedded systems
The Java compiler javac converts java text in machine independent byte code
Each machine or piece of hardware has a Java Virtual Machine (JVM) which converts byte code into machine code and executes it
Write once, run anywhere (slowly!)

61. Recap
Three types of people in computing:

62. Recap Three types of people in computing: End users – our customers
Applications programmers – people who understand a little about computers and write all the software the we use. Use C, C++, Java, VB
Hardware programmers/designers – people who know a lot about electronics, they built gadgets and the software the underpins the applications software. Use VHDL, assembler, C

63. Recap
What is a Computer?

64. Recap What is a Computer?
A big collection of electronic binary switches
The switches are actually very small transistors jammed onto silicon wafers - chips
CPU (Central Processing Unit)
Co-Processor (floating-point math, graphics)
Primary memory (RAM and ROM)
Disk controller
Input/Output devices and peripherals