QMCS 360 Class Notes, # 3	Dr. Rick Smith Quantitative Methods and Computer Science
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Homework Assignment - working it out

OS Evolution

Running without an OS

Loading a job

Copy from some storage device into RAM

Start it running

"Loader"

Running a job

Collecting "output"

Batching #1

Collect up 2 or more "jobs"

Running them in order - 1 by 1

Job "stops" and operator loads up the next one

Or, job jumps back to a monitor and loads the next one automatically

Batching #2

Collect up 2 or more "jobs"

Run them concurrently - "Multiprogramming"

Issues

Process management

Taking turns

No "Hogging the processor"

Memory management

Getting and using a specific amount

Option: Predefined amount

Option: Amount based on the job - specified in control

Option: Amount based on the program's size when loaded

Keeping your references to yourself - protection

Resource allocation - i/o

Keeping references to onesself

Deadlocking over excessive needs

Identifying files and devices ahead of time

Timesharing

People log in and dynamically demand more and more

Dynamic file access, device access, memory access

Security issues with remote access

Summary of OS capabilities

Proceess management

Taking turns to keep the processor busy

Taking turns to ensure that everyone finishes running

Don't focus on work that doesn't need hurry

Giving good response time

Memory management

Giving programs enough to get started

Keeping programs from banging on each other

Giving programs as much as they need within reason

I/O Management

Ensuring efficient operation

Ensure programs take turns in a fair manner

Prevent programs from interfereing with each other

File management

Give programs the essential functions (create, modify, rename, move, delete, etc.)

Provide protection as needed between users

Ensure that concurrent accesses work "correctly"

BREAK

PROCESSES

The simple case - Programs sharing RAM and hard drive

Take turns running while one is delayed

What makes one stop and the other run?

1. If one has run "too long" (quantum, time slice, ...)

2. If one is waiting for the hard drive

Process management data

When we stop a process, we have to save information about it

Program counter

Accumulators, registers

Stack pointer

Range of RAM being used

What it's waiting for (i/o, next "turn")

Process "state" - an indicator that the process is running, or why the process stopped

What is a state diagram?

Diagram with boxes indicating what the process is doing

Arrows indicate new "state" based on "events"

When an event occurs, the process may or may not change states

System may take some actions when a state needs to change

That's kind of a separate issue from the "state model" which really cares about events and states

The 2-state model (p. 115)

The 5-state model (p. 118)

Queueing models

Identify where a process needs to wait, insert a queue there.

Arrows indicate where a process goes after waiting in a queue.

A more complex case: "swapping" or "segmentation"

What if part of the program is missing, and must be read in from the hard drive?

Answer: you fix the state diagram to incorporate those issues

You also fix the process management data to include more info