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Initially short pieces of code to direct output
to a printer or accept input from a card reader. |
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Then background programs to handle requests from
multiple terminals and run multiple programs. |
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Now- |
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Device control |
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File maintenance (creation, deletion, naming,
grouping, transfer to and from disk) |
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Multitasking |
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Time Share (on larger machines) |
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Interface/presentation efforts (GUI) |
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Security |
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Major Examples |
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MS-DOS |
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Windows |
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MacOS |
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UNIX |
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Linux |
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Application Software - Computer programs that
perform work for a user |
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Initially written by users |
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Available languages – |
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Machine |
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Assembler |
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Procedural (Pascal, COBOL) |
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4GL |
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Common Elements of all languages: |
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Stored program concept |
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Flow of control |
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Sequence |
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Selection |
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Iteration |
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Subroutine |
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Assembler Example: |
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Pascal: J:= K + M |
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Assembler Equivalent: |
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mov ax, K |
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add ax, M |
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mov J, ax |
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Another Assembler Example: |
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Pascal:
J := K + M + N + P |
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Assembler Equivalent: |
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mov ax, K |
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add ax, M |
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add ax, N |
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add ax, P |
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mov J, ax |
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Pascal Example: |
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Readln(hrs); |
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If hrs > 40 |
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THEN grosspay := hrrate*40 + (hrs-40)*1.5*hrrate |
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ELSE grosspay:= hrs * hrrate; |
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Writeln(‘Gross pay was “,grosspay); |
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Dan Bricklin’s VISICALC |
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1978 - Harvard MBA student |
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Created a “spreadsheet” |
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Ran on Apple II computers |
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Little initial interest |
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Became software “tail” wagging the “hardware
“dog” (or “hardware drag”) |
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Branched out into VisiDex, Visigragh |
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Hired Mitch Kapor to program Visigraph |
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Kapor used pay and experience to create
Lotus-1-2-3 |
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Visicalc was not patented (software patents were
not legal until 1981) |
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Visicalc sold to Lotus in 1985 |
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and discontinued |
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Notes