Introduction to Computer Systems and Software

1
Introduction to Computer Systems and Software

• Lecture 1 of 2
• Simon Coupland
• simonc_at_dmu.ac.uk

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
Applications Programmers

• People who provide what end users want
• Little knowledge of hardware
• Appreciation for business logic
• Technically and generally mathematically literate

6
Low-Level Programmers and Hardware Designers

• Electronic engineers
• Computer scientists
• Knowledge of machine architecture
• Knowledge of electronics
• Real-time, bit manipulation and hardware
  resources
• Program in assembler and C
• Hardware design in FPGA, VHDL and more rarely
  ASIC

7
A Microcomputer System

• Three components
• Hardware
• Software
• Data

8
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

9
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

10
Data

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

11
Instruction and Data Storage

• Number representation (more in lecture 2)
• Fundamental to all computer system is the notion
  of a binary digit - 0 or 1 called a bit.
• Eight bits make up a byte.
• One or more bytes make up a word

12
Instruction and Data Storage

• Integers (a number with no decimal points)
• An unsigned byte range 0 to 255

• 01001101 1 4 8 64 77
• 10111101 1 2 8 16 32 128 187

13
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 -128 result

• 01001101 1 4 8 64 77
• 11001101 -128 1 4 8 64 -51

14
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

15
Characters (text)

• Text is a collection (an array) of characters
• Generally characters are encoded in ASCII
  (American Standard Code for Information
  Interchange)
• Example Hi!

16
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

17
Low Level Computer Languages

• Assembly language
• Example on MC680000 series
• CLR.W D3

• Clear the lower 16 bit the data register D3

18
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

19
High Level Computer Languages

• Example in C
• int D0 7 2 (267 23)

• Equivalent in MC680000 assembler
• MOVE.L 267,D0
• SUB.W 23,D0
• ADD.W D0,D0
• ADD.W 7,D0

20
Technology and Computer Evolution
21
Computer Generations

• Computer systems are large collections of
  electronic switches
• The power of a computer depends on the number of
  these electronic binary switches

22
Computer Generations

• First Generation (1940s)
• 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

23
Computer Generations

• Thermionic valve / vacuum tube

24
Computer Generations

• Second Generation (1950s)
• 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
• Dont breakdown

25
Computer Generations

• The Transistor

Collector
Emitter
Base
26
Computer Generations

• Third Generation (1960s)
• Switches were fabricated into small scale
  integrated circuits (ICs)
• Still use semiconductors
• Many transistors built onto a single chip
• Much smaller
• More processing power

27
Computer Generations

• Forth Generation (1970s to date)
• Miniaturization is the key
• Small scale integration 2 - 64 transistors
• Medium scale integration 64 - 2000 transistors
• Large scale integration 2000 - 64000 transistors
• Very large scale integration 64K 200K
  transistors
• Ultra large scale integration 200K 100M
  transistors

28
Computer Generations

• Moores Law
• Gordon Moore co-founder of Intel
• Transistor density on ICs will double every
  eighteen months

29
Computer Generations
30
Computer Generations

• Moores 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

31
Computer Hardware
32
Computer Hardware
33
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

34
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

35
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

36
Computer Hardware

• Memory
• Organised as a table

37
Computer Hardware

• Inside the CPU

ALU
Control unit
Clock
Pipeline
Internal cache memory
RAM
External cache memory
Data
Address
Control
38
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

39
Computer Hardware

• Inside the CPU Fetch/Excute
• Fetch
• 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.

40
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

41
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

42
Computer Software
43
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

44
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

45
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

46
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!)

47
Recap

• Three types of people in computing

48
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

49
Recap

• What is a Computer?

50
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