MIS 5241 SOFTWARE

MIS 5242 Agenda The Stored Program Concept Software as Control Software as Simulation

MIS 5243 The Stored Program Concept Commands or instructions for a CPU are stored as “data” sequentially in packages called “programs.” This allows rapid access to programs as well as the ability to create or generate them at will by changing the “data” Some programs “write” other programs (these are called compilers), while other programs can even modify themselves. Having programs as data makes them very portable and so long as the CPU can interpret the instructions, programs can move into and out of and even between computers Get 17 If zero, go to 10 Get 16 Put into 10 Get 15 Subtract “1” If zero, go to 10 Put into 15 Go to 5 Stop Add “1” Put into 17 If zero, go to 10 Go to 1 5 Get 14 -5

MIS 5244 Instructions determine the “flow” of action of the CPU. The instructions don’t have to be purely mathematical. Some can control equipment (printers, screens, eg.) Compute Test Compute Test Software as Control Iteration Sequence Alternation

MIS 5245 Software Controls Software, Too Software can control other items of software In addition to compilers that create other software, an operating system controls other programs (and data). These “control programs” differ in the kinds of resources they control and the human interface for human intervention.

MIS 5246 (Computer) Operating System Operating System (DOS, Linux Windows Unix, etc.) Inter- face (text or GUI) System Resources: Files, i/o devices, storage devices, communication lines, memory, time This is also a system resource This is an operating system for a computer. But if the resources are not computer resources, it’s still an operating system, simulating according to some set of rules or plan

MIS 5247 Software as Simulation Because software is really expression of control, to the extent that software can control an environment or situation and its resources, it can simulate activities within that environment Software can thus make a general purpose computer look like any specific computer.

MIS 5248 A simulation General Purpose Computer Software Human Interaction Primary Input Primary (Data) and Secondary (Device) Outputs Control State- ments Describing New Situation Humans can provide input to “control” simulation or they can just be participants in the simulated environment

MIS 5249 Layers of Software Hardware Resources, including Data Software that Controls Devices Software that Controls Humans Operating System Application Software

MIS Software upon Software Any Software Some Other Software Give me service! I want this and this and this. I want results!! Here are the results! I don’t care what you do with them!! The black box principle Question: What does this remind you of?????

MIS Software Flexibility Because of the black box principle, software can be used to bundle (i.e., control) other software Thus new bundles can be created, and reused. If these bundles are commonly referred to business concepts, they are called “objects” An entire programming method exists to take advantage of this bundling principle, called Object Oriented Programming.

MIS Types of Software System controllers: Operating systems Software generators: Compilers, languages Virtual environments: Simulators Personal software: Productivity tools Data management: Database managers High-level command at a time: Script Hardware interpreters: Drivers Operating environments: Shells

MIS Software People Software builders = programmers Programmers who work on systems: system programmers Programmers who work on problems: programmer/analysts Programmers who work on user applications: application programmers

MIS Systems People High on need for achievement Low on social needs Probably more introverted than users Rational Judgmental Somewhat intuitive and artistic too, though Thinking rather than feeling

MIS Time for a Joke (Basis) Three people, a system manager, a systems analyst and a programmer are driving through the mountains. (Crisis) Suddenly at the top of the pass, the brakes fail (Thesis) The car narrowly misses falling off the mountain and comes to a stop against a big tree swaying over a precipice. They are in trouble! (Problem) How to get out of trouble….

MIS System Manager: Look at the car’s operating manual and see what it says about keeping a car from falling off a mountain; possibly shutting down the car Systems Analyst: Examine the cars specifications to see what might have failed to cause the braking problem. Programmer…..