Computer Software

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Computer Software
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How Programs Direct the CPU

• the typical CPU is designed to perform basic
  arithmetic, logic, and data transfer operations
• a program is a list of instructions that direct
  the processing of the computer
• programs are stored in memory and executed
  step-by-step by the CPU

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Machine Language
Machines Native Language
Machine Dependent
10101010100010100101011010110110101101010100111110
10101010011001110111110110111110111001100001011111
10111111101110101110101111011011011101001101
No Documentation
Unreadable by Normal Humans
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First GenerationAssembly Instruction Set

• assembly languages are symbolic versions of the
  native machine code

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First GenerationAn Assembly Program
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Programming Languages

• ASSEMBLY LANGUAGES
• 11 representations of host processor machine
  code
• symbolic representations
• not portable

• HIGH LEVEL LANGUAGES
• 1many representations of the machine code
• more abstract
• portable (with translation programs)

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Second GenerationHigh Level

• FORTRAN
• Do 100 I 1, 10
• PRINT , I
• 100 CONTINUE

• COBOL
• 100-PERFORM 200-PRINT-NUMBERS
• UNTIL COUNT IS EQUAL 10
• 200-PRINT-NUMBERS.
• ADD 1 TO COUNT
• MOVE COUNT TO DETAIL-LINE
• WRITE DETAIL-LINE
• AFTER ADVANCING 1 LINES

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Second Generation

• BASIC
• 100 For I 1 to 10
• 110 PRINT I
• 120 NEXT I

• PASCAL
• FOR I 1 TO 10 DO
• WRITE(I2)
• C
• For ( i1 i lt 11 i)
• printf (d, i)

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Third Generation

• SQL (Structured Query Language)
• SELECT first,last, address ,city,state,zip
• FROM Customers
• WHERE city Asheville
• ORDER BY last,first

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Fourth GenerationNatural Language

• In MS Help type
• Show me any help on how to hide this obnoxious
  office assistant below

RESULTS Display tips and messages through
Office Assistant Troubleshoot online meetings
Hide Office Assistant Troubleshoot Office
Assistant
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Programming Languages
Flash / XML

• Selecting the right language
• Space available
• Speed required
• Organizational resources available
• Type of target application

ASP / JSP
JavaScript VBScript
Visual Basic
HTML
C / C
Java
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Software

• How are programs created?

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System Development Life Cycle
System Development Life Cycle
Problem/ Opportunity Identification
Analysis
Design
Development Documentation
Testing Installation
Maintenance Evaluation
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Program Development Cycle

• ANALYSIS SPECIFICATION
• understanding the process or problem
• deciding on requirements and features

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Program Development Cycle

• DESIGN
• devising a plan
• dividing tasks into program components
• writing algorithms for program components

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Flowchart and Pseudocode
Flowchart
Pseudocode
Bold terms show actions that are common in
programming, such as reading data, making
decisions, printing, and so on.
1. Ask the user how many hours they worked
today 2. If the number of hours worked lt 8,
compute total pay without overtime otherwise,
compute total pay with overtime pay 3. Print
total pay
Underlined words are information items that
appear repeatedly in the algorithm.
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Program Development Cycle

• CODING
• employing symbolic programming languages as an
  aid
• translating algorithms into executable programs

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Program Development Cycle

• TESTING CORRECTION
• assembling/testing program components
• testing the system
• maintenance revising the system to meet new
  specifications

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Testing Software

• In house completed version is called
• Alpha version
• A complete version sent out to users to test
• Beta Version

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Programming Language

• a program is a list of statements in a
  programming language
• programs are symbolic representations of
  computational processes
• programs are translated to machine code for
  execution on a given processor

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Programming Languages

• Interpreter
• Translates each line of code, each time it is
  run.
• Example
• Loan.bas

• Compiler
• Translates source code into machine exeutable
  language.
• Examples
• Powerpnt.cc
• Powerpnt.exe

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Software Complexity

• tasks that software systems model are often
  complicated and not well understood
• scale of software systems is often too great for
  a single person to comprehend and manage
• software systems components interact in
  unpredictable ways

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Risks of Software

• Mariner I Atlas booster fails (18 million)
• Mariner 8 probe lost
• Therac X-ray system kills two and injures others
• Over 1,000 British cancer patients are underdosed
  in radiation therapy
• Airbus 320 crashes due to control system problems
• Audi 5000 recalled after 250 accidents blamed on
  computer-controlled system malfunction
• Mars Probe

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Who is at Risk

• Analyst?
• Designer ?
• Coder ?
• Tester ?
• Software Company ?
• User ?
• Consumer ?

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