1. computers introduction

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Lecture 1: IntroductionLecture 1: Introduction
 OverviewOverview
 History of ComputersHistory of Computers
 Application AreasApplication Areas
 Types of ComputersTypes of Computers
 Computer ConfigurationsComputer Configurations
 Computers as Information ProcessorsComputers as Information Processors

22
IntroductionIntroduction
 Basic Machine Hardware ArchitectureBasic Machine Hardware Architecture
 CPUCPU
 Memory/StorageMemory/Storage
 Main MemoryMain Memory
 Input/Output DevicesInput/Output Devices
 Basic Machine SoftwareBasic Machine Software
 FlowchartsFlowcharts
 LanguagesLanguages
 Operating SystemsOperating Systems
 System UtilitiesSystem Utilities
 ApplicationsApplications

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Overview of Part 1Overview of Part 1
 Number system:Number system: how is informationhow is information
represented in a computer.represented in a computer.
 Boolean Algebra:Boolean Algebra: the basis for logic designthe basis for logic design
and manipulation of information.and manipulation of information.
 Logic gates:Logic gates: what are the gates used, andwhat are the gates used, and
how circuits can be made from gates.how circuits can be made from gates.
 Function simplification:Function simplification: to reduce the sizeto reduce the size
of design, increase speed, etc.of design, increase speed, etc.

44
Overview of Part 1Overview of Part 1
 Combinational circuits:Combinational circuits: simple circuitsimple circuit
design without memory.design without memory.
 Sequential circuits:Sequential circuits: circuit design withcircuit design with
memory.memory.
 Disk:Disk: storage techniques.storage techniques.
 Bus:Bus: internal communication.internal communication.
 I/O:I/O: devices, technology, etc.devices, technology, etc.

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History of ComputersHistory of Computers
 AbacusAbacus invented in Babylonia in 3000BCinvented in Babylonia in 3000BC
 Adding machineAdding machine byby Blaise PascalBlaise Pascal (1642)(1642)
 Difference engineDifference engine and theand the analytical engineanalytical engine byby
Charles BabbageCharles Babbage (1842)(1842)
 IBM first electromechanical computer (usingIBM first electromechanical computer (using
relays) designed byrelays) designed by Howard AikenHoward Aiken (1937) was(1937) was
based on punched cards.based on punched cards.
 used to calculate tables of mathematical functionsused to calculate tables of mathematical functions

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 11stst
Generation ComputersGeneration Computers (1940s to early 1950s) –(1940s to early 1950s) –
based onbased on vacuum tubesvacuum tubes technology.technology.
 1943 – ENIAC: first fully electronic computer, designed by1943 – ENIAC: first fully electronic computer, designed by
John MauchlyJohn Mauchly
 1944 – Mark I: Howard Aiken1944 – Mark I: Howard Aiken
 1946 – EDVAC: first stored program computers, designed by1946 – EDVAC: first stored program computers, designed by
John von NeumannJohn von Neumann
 22ndnd
Generation ComputersGeneration Computers (late 50s to early 60s) –(late 50s to early 60s) –
based onbased on transistorstransistors technology.technology.
 more reliable, less expensive, low heat dissipationmore reliable, less expensive, low heat dissipation
 IBM 7000 series, DEC PDP-1IBM 7000 series, DEC PDP-1

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 33rdrd
Generation ComputersGeneration Computers (late 60s to early 80s) –(late 60s to early 80s) –
integrated circuitsintegrated circuits (IC).(IC).
 IBM 360 series, DEC PDP-8IBM 360 series, DEC PDP-8
 IC – many transistors packed into single containerIC – many transistors packed into single container
 low prices, high packing densitylow prices, high packing density
 44thth
Generation ComputersGeneration Computers (present day) LSI/VLSI(present day) LSI/VLSI
 small size, low-cost, large memory, ultra-fast PCs tosmall size, low-cost, large memory, ultra-fast PCs to
supercomputerssupercomputers
 55thth
Generation ComputersGeneration Computers (future)(future)
 massively parallel, large knowledge bases, intelligentmassively parallel, large knowledge bases, intelligent
 Japan, Europe and US advanced research programsJapan, Europe and US advanced research programs

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 Web sitesWeb sites
 History of ComputersHistory of Computers
(http://www.comp.nus.edu.sg/~sf100/c1f7.htm)(http://www.comp.nus.edu.sg/~sf100/c1f7.htm)
 ACM Timeline of Computing HistoryACM Timeline of Computing History
(http://www.computer.org/computer/timeline)(http://www.computer.org/computer/timeline)
 The Virtual Museum of ComputingThe Virtual Museum of Computing
(http://www.comlab.ox.ac.uk/archive/other/museums/computi(http://www.comlab.ox.ac.uk/archive/other/museums/computi
ng.html)ng.html)
 IEEE Annals of the History of ComputingIEEE Annals of the History of Computing
(http://www.computer.org/annals/)(http://www.computer.org/annals/)
 and others (surf the web)and others (surf the web)

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Application AreasApplication Areas
 Scientific:Scientific: weather forecasting, simulation, space-weather forecasting, simulation, space-
program.program.
 one of the earliest application areas.one of the earliest application areas.
 heavy computation but small amount of data.heavy computation but small amount of data.
 Commercial:Commercial: accounting, banking, inventory, sales.accounting, banking, inventory, sales.
 changes nature of business – information is money.changes nature of business – information is money.
 high data throughput, simple calculations.high data throughput, simple calculations.
 Manufacturing:Manufacturing: numerical control, CAD/CAM,numerical control, CAD/CAM,
integration.integration.
 graphics, interfacing, device-drivers, networks.graphics, interfacing, device-drivers, networks.

1010
Application AreasApplication Areas
 Real-time & Control System:Real-time & Control System: air-traffic control,air-traffic control,
aircraft,nuclear power station.aircraft,nuclear power station.
 real time, very fast, safety-critical.real time, very fast, safety-critical.
 Educational & RecreationalEducational & Recreational
 CAI software, multi-media, games, Internet, World WideCAI software, multi-media, games, Internet, World Wide
Web.Web.
 TelecommunicationTelecommunication
 Network, SCV, Singapore One.Network, SCV, Singapore One.

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Types of ComputersTypes of Computers
 Supercomputers:Supercomputers:
 very fast (Gflops) but expensive machine($10m), vector orvery fast (Gflops) but expensive machine($10m), vector or
parallel processors, used in scientific applications andparallel processors, used in scientific applications and
simulations.simulations.
 Mainframes:Mainframes:
 fast (>10mips) but expensive ($1m), high-throughput, usedfast (>10mips) but expensive ($1m), high-throughput, used
in large commercial organisations, support many concurrentin large commercial organisations, support many concurrent
users interactively.users interactively.
 Mini-computers:Mini-computers:
 fast but affordable ($200k), used in medium-sizedfast but affordable ($200k), used in medium-sized
organisations (e.g. SoC), support multiple users.organisations (e.g. SoC), support multiple users.

1212
Types of ComputersTypes of Computers
 Workstations:Workstations:
 affordable ($20k) and fast single-user systems (20 riscsaffordable ($20k) and fast single-user systems (20 riscs
mips), good graphics capabilities, engineering, network-mips), good graphics capabilities, engineering, network-
based computing.based computing.
 Micro/Personal/Home Computers:Micro/Personal/Home Computers:
 cheap and affordable ($3k), transportable, home use, goodcheap and affordable ($3k), transportable, home use, good
for games and as educational tool, word processing, suitablefor games and as educational tool, word processing, suitable
for small enterprise.for small enterprise.

1313
Computer ConfigurationsComputer Configurations
 Stand-alone computer systemStand-alone computer system
 Modem connectionModem connection

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 Terminals-host connectionsTerminals-host connections

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 Network of computersNetwork of computers

1616
Computers as InformationComputers as Information
ProcessorsProcessors
Example: An automobile
augments our power of
locomotion.
A computer is a device
capable of solving problems
according to designed
program. It simply augments
our power of storage and
speed of calculation.
Driver
Programmer

1717
Computers as InformationComputers as Information
 Unlike previous inventions, computers are specialUnlike previous inventions, computers are special
because they arebecause they are general-purposegeneral-purpose..
 Could be used to perform a variety of tasks.Could be used to perform a variety of tasks.
 Computer =Computer = Hardware + SoftwareHardware + Software..
 HardwareHardware: physical components for computation/processing;: physical components for computation/processing;
should be simple, fast, reliable.should be simple, fast, reliable.
 SoftwareSoftware: set of instructions to perform tasks to: set of instructions to perform tasks to
specifications; should be flexible, user-friendly,specifications; should be flexible, user-friendly,
sophisticated.sophisticated.

1818
Computer as InformationComputer as Information
Computer are Information Processors
Data Units:
1 bit (binary digit): one of two values (0 or 1)
1 byte: 8-bits
1 word: 1, 2, or 4 bytes, or more (depends on ALU)
Computer
system
Raw
data
Processed
information

1919
Basic Machine HardwareBasic Machine Hardware
ArchitectureArchitecture
 Main Components:Main Components:
 CPUCPU (Central Processing Unit: controls devices and(Central Processing Unit: controls devices and
processes data).processes data).
 MemoryMemory: stores programs and intermediate data.: stores programs and intermediate data.
 Input DevicesInput Devices: accept data from outside world.: accept data from outside world.
 Output DevicesOutput Devices: presents data to the outside world.: presents data to the outside world.
 An analogy with Human Information Processors:An analogy with Human Information Processors:
 CPU – brain’s reasoning powersCPU – brain’s reasoning powers
 Memory – brain’s memoryMemory – brain’s memory
 Input Devices – eyes, ears, sensory sub-systemInput Devices – eyes, ears, sensory sub-system
 Output Devices – mouth, hands, facial and bodyOutput Devices – mouth, hands, facial and body
expressionsexpressions

2020
Monitor
(Output)
Mouse and Keyboard (Input)
Headphone
(Output)
Hardware box
(contains
processor, memory,
buses etc.)

2121
Motherboard
(Printed Circuit
Board)
Processor
Slots for RAM chips
Network card and
CRT card
Cage for
mounting drives
Floppy disk
drive and
Hard disk
drive
© above picture: Patterson and Hennessy

2222
Hardware – CPUHardware – CPU
 CPU = control unit + ALU + registersCPU = control unit + ALU + registers
 Control Unit :Control Unit : monitors and directs sequences ofmonitors and directs sequences of
instructionsinstructions
 Execution CycleExecution Cycle (repeated):(repeated):
 fetch (next instruction)fetch (next instruction)
 decodedecode
 executeexecute

2323
 ALU:ALU: performs simple arithmetic and logicalperforms simple arithmetic and logical
operations.operations.
 Examples: Add, subtract, and, or, invert, increment etc.Examples: Add, subtract, and, or, invert, increment etc.
A B
ALU
select
R = A op B
n-bits operations
R

2424
 Registers:Registers: temporary results + status informationtemporary results + status information
 ACC (accumulator) – current dataACC (accumulator) – current data
 PC (program counter) – points to next instructionPC (program counter) – points to next instruction
 IR (instruction register) – current instructionIR (instruction register) – current instruction
 MA (memory address) – address to read/writeMA (memory address) – address to read/write
 MB (memory buffer) – data to read/writeMB (memory buffer) – data to read/write

2525
Hardware – Memory/StorageHardware – Memory/Storage
 Purpose: to store program and data.Purpose: to store program and data.
 Desirable Traits: fast access, large capacity,Desirable Traits: fast access, large capacity,
economical, non-volatile.economical, non-volatile.
 However, most memory devices do not have all theseHowever, most memory devices do not have all these
traits.traits.

2626
Hardware – Memory/StorageHardware – Memory/Storage
 Solution: hierarchical combinationSolution: hierarchical combination
registers
main memory
disk storage
magnetic tapes
Fast, expensive
(small numbers),
volatile
Slow, cheap
(large numbers),
non-volatile

2727
Hardware – Main MemoryHardware – Main Memory
 FastFast BUTBUT volatilevolatile (need power to maintain data)(need power to maintain data)
 Logical structure – table of memory cells/units.Logical structure – table of memory cells/units.
0
1
2
3
2m
-3
2m
-2
2m
-1
addresses
memory
cells
8 bits or more
M
A
R
M
B
R
address
data

2828
Hardware – Main MemoryHardware – Main Memory
 Memory cells may be grouped intoMemory cells may be grouped into pagespages (say 512(say 512
consecutive words per page).consecutive words per page).
 UnitsUnits
 1 KBytes = 1024 (or 21 KBytes = 1024 (or 21010
) bytes) bytes
 1 MBytes = 1024 Kbytes (or 21 MBytes = 1024 Kbytes (or 22020
bytes)bytes)
 1 GBytes = 1024 Mbytes (or 21 GBytes = 1024 Mbytes (or 23030
bytes)bytes)

2929
Hardware – Input/OutputHardware – Input/Output
DevicesDevices
 Input devicesInput devices: read/accept data (into computer): read/accept data (into computer)
 obsolete: card reader, paper tape readerobsolete: card reader, paper tape reader
 present: keyboard, mouse, light-pen, optical char readerpresent: keyboard, mouse, light-pen, optical char reader
 future: voice and vision recognition.future: voice and vision recognition.
 Output devicesOutput devices: write/display data (to users): write/display data (to users)
 obsolete: card & paper punch, teletypeobsolete: card & paper punch, teletype
 present: VDU (visual display unit), printers, plotters,present: VDU (visual display unit), printers, plotters,
graphics display, soundgraphics display, sound
 future: voice synthesis.future: voice synthesis.

3030
Basic Machine SoftwareBasic Machine Software
 SoftwareSoftware is the key to making computers generalis the key to making computers general
purpose.purpose.
 Software are often built hierarchically, with layers ofSoftware are often built hierarchically, with layers of
software providing successive higher-level ofsoftware providing successive higher-level of
abstractions.abstractions.
 This structure is reflected by the following onion layerThis structure is reflected by the following onion layer
view of software.view of software.

3131
Basic Machine SoftwareBasic Machine Software
Hardware
Operating system
System utilities
Applications/User programs

3232
Software – FlowchartsSoftware – Flowcharts
 The sequence of instructions of a software/programThe sequence of instructions of a software/program
can be graphically specified usingcan be graphically specified using flowchartsflowcharts..
 The flowchart technique maybe a little outdated butThe flowchart technique maybe a little outdated but
could still be used in a clear manner for simplecould still be used in a clear manner for simple
problems.problems.
 As an example, the procedure to find the roots of aAs an example, the procedure to find the roots of a
quadratic equation,quadratic equation, axax22
++ bxbx ++ cc = 0, can be written= 0, can be written
using the following equation:using the following equation:
aacbbroots 2/)4( 2
−±−=

3333
Software – FlowchartsSoftware – Flowcharts
 This procedure can be coded in the followingThis procedure can be coded in the following
flowchart:flowchart:
aacbbroots 2/)4( 2
−±−=
Read
a,b,c
a=0?
d:=b2
- 4ac
d>0
d=0
d<0
Write
real root
Write
complex roots
Write
real roots
= <
>
no
yes Write
not quadratic

3434
Software – LanguagesSoftware – Languages
 All programs will have to be coded in someAll programs will have to be coded in some
programming language – usually text-based.programming language – usually text-based.
 The native language of machine is calledThe native language of machine is called machinemachine
languagelanguage..
 This consists of a set of primitive instructions, codedThis consists of a set of primitive instructions, coded
in numbers.in numbers.
 An example is "0310 0412 0512". But can youAn example is "0310 0412 0512". But can you
understand what it does?understand what it does?

3535
 Possible to use more human-readable mnemonicPossible to use more human-readable mnemonic
instructions.instructions.
 These are know asThese are know as assembly languageassembly language instructions.instructions.
 Normally, assembly language has a 1-to-1Normally, assembly language has a 1-to-1
correspondence with machine language.correspondence with machine language.
Mnemonic Description
ADD 10 AC:=AC+C(10)
SUB 12 AC:=AC-C(12)
STO 12 C(12)=AC

3636
 Assembly language is still very primitive.Assembly language is still very primitive.
 Higher-level LanguagesHigher-level Languages, like Pascal, C, Fortran,, like Pascal, C, Fortran,
which are a little closer to English language havewhich are a little closer to English language have
been developed.been developed.

3737
 An example Pascal program to find roots of quadraticAn example Pascal program to find roots of quadratic
equation:equation:
read(a,b,c);
if a=0
then writeln ("not a quadratic equation")
else
begin
d := sqr(b)-4*a*c;
if d>0 then writeln ("complex roots")
else if d=0 then writeln("single root =",-b/(2*a))
else writeln ("root1=",-b+sqrt(d)/(2*a),
"root2=", -b-sqrt(d)/(2*a));
end;

3838
Software – Operating SystemsSoftware – Operating Systems
 Operating SystemOperating System (OS) is situated directly above(OS) is situated directly above
hardware. It controls and manages the availablehardware. It controls and manages the available
hardware resources.hardware resources.
 Often, OS has special access privileges to certainOften, OS has special access privileges to certain
categories of instructions and certain hardwarecategories of instructions and certain hardware
 User programs have to go through OS for theseUser programs have to go through OS for these
privileges.privileges.

3939
Software – Operating SystemsSoftware – Operating Systems
 Associated Functions/Tasks:Associated Functions/Tasks:
 boots up machineboots up machine
 loads user programloads user program
 allocates main memory/storage spaceallocates main memory/storage space
 schedules concurrent user programsschedules concurrent user programs
 drivers to service various devices (terminals, printers, etc.)drivers to service various devices (terminals, printers, etc.)

4040
Software – System UtilitiesSoftware – System Utilities
 Above the OS, there is a set of frequently executedAbove the OS, there is a set of frequently executed
programs,calledprograms,called System UtilitiesSystem Utilities. These utilities are. These utilities are
often packaged with OS.often packaged with OS.
 Used by programmers/analyst to help develop applications.Used by programmers/analyst to help develop applications.
 Some examplesSome examples
 EditorEditor:: compose/edit user programs or data filescompose/edit user programs or data files
 Assembler:Assembler: translates assembly to machine codetranslates assembly to machine code
 Compiler:Compiler: translates high-level language totranslates high-level language to
assembler/machine codeassembler/machine code
 Spooler:Spooler: temporary stores print files for queuingtemporary stores print files for queuing

4141
Software – System UtilitiesSoftware – System Utilities
 Some examples (continued)Some examples (continued)
 Mailer:Mailer: forwards/receives mails between usersforwards/receives mails between users
 DBMSDBMS (Data-Base Management System): centralised(Data-Base Management System): centralised
management of data at a more abstract level than filesmanagement of data at a more abstract level than files
 Window Management System:Window Management System: multiple windows can appearmultiple windows can appear
on single screen. These together with various graphicalon single screen. These together with various graphical
entities (e.g. menus,panels, buttons) can be managed byentities (e.g. menus,panels, buttons) can be managed by
WMS.WMS.

4242
Software – ApplicationsSoftware – Applications
 Word-ProcessorsWord-Processors: compose/edit reports/articles: compose/edit reports/articles
 Accounting PackageAccounting Package: keeps track of accounting: keeps track of accounting
transactions, produces daily/weekly/monthlytransactions, produces daily/weekly/monthly
(profit/loss) reports(profit/loss) reports
 Inventory SystemInventory System: keeps track of stock levels: keeps track of stock levels
 Personnel/Payroll SystemPersonnel/Payroll System: staff records, monthly: staff records, monthly
salarysalary

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