A brief history of Software

• Machine Language and generation zero
  • Each machine has it's own language
    • Assume you have 10 boxes labeled a through j
    • Assume 1 means add, 2 subtract, 3 multiply, 4 divide
    • so 1 a b c means to add the number at a to the number at b and store the result at c
    • Assume 5 means input, so 5 a means to read a number and store it at a
    • Assume 6 means to output, so 6 b means to print the number stored at b
    • each of these is an instruction
    • Consider the following program

      5a
      3aab
      3bbc
      6a
      6b
      6c
      	   

    • The problem is, we store this in binary, so it might look like

      1010000 0110000 0000000 1011000
      1000100 1011000 0011000 0111000
      1000000
      	   

    • Programmers had to produce this series of numbers
    • Mistakes were common
• Generation 1, Assembly language
  • Mnemonics were established (ADD = 1, SUB = 2, IN = 5)
  • Programs were written in this new language

    IN a
    MULT a a b
    MULT b b c
    OUT a
    OUT b
    OUT c
    	

  • A translator (or assembler) changed from the human readable assembly to the machine code above.
  • The assembler is an example of a systems program
• Generation 2, high level languages
  • Written more like mathematics (FORTRAN)

    	    READ a
    	    b = a * a
    	    c = b * b
    	    WRITE a,b,c
    	

  • Or English (COBOL)

    	    Input a
    	    Multiply a by a giving  b
    	    Multiply b by b giving  c
    	    Output a, b, c
    	

  • We gain a level of abstraction here,
  • A compiler translates the entire program into machine language then it is run
  • or a interpreter translates and runs a single line at a time (BASIC)
  • Application Programs are programs that are not related to running the system, but to performing a function.
• The third generation
  • More systems level programs are written
  • More free computer time, (faster lower cost computers)
  • More expensive programmers (more computers, few people know how to do this)
  • Loaders, Linkers
  • Operating System
  • Multitasking, time sharing, multiuser
  • SPSS - a programmable package written in fortran for statistics
  • Users are less close to hardware, and are not the programmers
• The fourth Generation
  • Structured Programming Languages -
    • More powerful than first generation languages
    • C, Pascal, Modula-2
    • More abstractions
  • Better OS
    • UNIX, DOS
    • GUI
  • Applications start to grow
    • Spreadsheets
    • Word processors
    • Data Base Management Systems
• The Fifth Generation
  • Object Oriented Design
    • C++
    • Java
  • Much more network integration
  • Network Applications
    • WWW
    • email
  • User is mostly unaware of the computer/network
  • embedded systems
    • The computer inside your _____
• Where will it go?
  • Things will continue to get faster
  • More layers of abstraction will be added
  • More things will network, (wireless)