Transcript Computer

Chapter 1
Introduction
Computer Science/Ch.1 Introduction
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Who is the user ?
• Computer professional :
– has formal education in the technical aspects of
using computers.
– eg. programmer, systems analyst, or computer
operator.
• User :
– someone without much technical knowledge of
computers but who makes decisions based on
reports and other results that computers produce.
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What is a computer system?
• Computer:
– combination of electronic and electro-mechanical
components.
– has no intelligence
– hardware
• Computer system:
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–
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hardware
software
data/information
procedure
people
• Software:
– the instructions that tell the hardware how to perform a
task.
• Data:
– raw, unevaluated facts and figures, concepts or
instructions.
• Information : the product of data
processing
input
computer
data
data process
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output
information
Computer Hardware
• Input hardware:
– to collect data and convert it into a form suitable for
computer processing.
– eg. keyboard, mouse, scanner.
• Storage hardware:
– stores software and data in a form that is easy to retrieve
and relatively permanent, or nonvolatile; i.e, data is not
lost when power is turned off.
• Processing hardware:
– retrieves, interpretes, executes software instructions
provided to the computer.
– CPU (Central Processing Unit):
» Arithmetic/Logic Unit
» Control Unit
– Main memory
• Output hardware:
– displays information produced by the computer system
in either hardcopy or softcopy output.
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Computer Software
• Software:
– a group of related programs, each of which contains
instructions that perform specific tasks.
• System software:
– programs designed to allow the computer to manage its
own resources.
– OS, Compiler ...
• Application software:
– programs that tell the computer how to satisfy the users'
specific needs.
– software packages, games.
– Accounting, Payroll, Inventory, etc.
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Types of computer systems
• Supercomputers:
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handle gigantic amounts of scientific computation.
up to 50,000 times faster than a microcomputer.
cost up to $20 million.
defense and weaponry, weather forecasting, NASA.
ETA-10, CRAY X-MP.
• Mainframe computers:
– support the processing requirements of hundreds or
thousands of users.
– cost up to $10 million.
– banks, airline, and universities.
– CYBER 172, IBM 3491.
• Minicomputers:
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support from 2 to 50 users.
cost up to several hundred thousand dollars.
small and medium-sized companies.
HP 9000
• Microcomputers: (Personal Computer)
– cost $500 to $15,000.
– use microprocessor chip as its CPU.
• Workstations:
– faster, more graphics abilities.
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Types of computer operations
• Batch processing : Do it later
• On-line processing : Do it now
– computer can immediately access and process the input
data
– multi-user: interactive time-sharing
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Categorizing a computer
• Type of CPU
• Amount of main memory the CPU can
use
• Capacity of the storage devices
• Speed of the output devices
• Processing speed in MIPS
– MIPS: million of instructions per second
• Number of users that can access the
computer at a time
• Cost of a computer system
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The evolution of computers
• First generation: 1944-1958
– vacuum tubes, punched cards, magnetic tapes.
– ENIAC (1946)
• Secord generation: 1959-1963
– transistors, solid-state devices.
• Third generation: 1964-1970
– integrated circuits (complete electronic circuits on a
silicon chip).
– magnetic disks
– operation systems and application software.
• Fourth generation: 1971-now
– Large-Scale Integration (LSI) circuits.
– keyboard, microprocessors
• Fifth generation: Now and in the future
– VLSI (Very Large-Scale Integration) of circuits.
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Computer uses
• Business
– Inventory, Personnel, Payroll, Accounting, Investment...
• Government
• Medicine
– CAT : computerized axial tomography
• Education
– CAI : computer assisted instruction
• Industry
– CAD : computer aided design
– CAM : computer aided manufacture
• Entertainment and sports
– computer graphics
• Agriculture
• Home
– game
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Programming Language
• machine instruction
– operation code
– operand
• program : a sequence of instructions
• program language
– high level language : PASCAL, C, FORTRAN,COBOL...
– low level language : Assembly language
software
computer
hardware
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Program execution
• Source program:
– a program which can not be executed by the computer
• Object program:
– a program which is translated from the source program
and can be executed by the computer
Source
Program
computer executing
compiler program
compilation
time
Object
Program
computer executing
object program
Program
Output
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running time
Problem solving
problem
solving phase
Problem
Solution in
Algorithm
difficult step
Computer
Program
Computer Science/Ch.1 Introduction
implementation
phase
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Problem solving - steps
• Design an algorithm
• Implement the algorthm by a language
• Algorithm :
– a step-by-step process (finite steps)
• Expression of algorithms:
– Narrative description
– Flow chart
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Flow Chart
Start/
Stop
Compute
Decision
Input
Output
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Flow Chart - Example
Start
Input
Compute
No
Yes
?
Output
Output
Stop
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