Mid Term review

CSC345

• What is an Operating System?

• Various systems and their pros and cons– E.g. multi-tasking vs. Batch

• OS definitions– Resource allocator– Control program– Kernel

Abstract View of System Components

Important OS Features/services

• Process Management (CPU scheduling)• Main Memory Management• File Management• I/O System Management• Secondary Management• Networking• Protection System• Command-Interpreter System

OS Control Structure

Memory

I/O

File

Processes

Memory Tables

I/O Tables

File Tables

Process 1Process 2

…

Process N

Primary Table

Process Image

User dataUser programSystem stack

PCB

Process State Diagram

Ready

BlockedSuspend

New Running

Exit

release

dispatch

time-out

eventactivate

suspend

admit

wait

• System call vs. System program

Chapter 2: Computer-System Structures

• Computer System Operation

• I/O Structure

• Storage Structure

• Storage Hierarchy

• Hardware Protection

• General System Architecture

Two I/O Methods

Synchronous Asynchronous

Dual mode operation & why ?

Use of A System Call to Perform I/O

Use of A Base and Limit Register

Hardware Address Protection

OS structure & Layered Approach

• The operating system is divided into a number of layers (levels), each built on top of lower layers. The bottom layer (layer 0), is the hardware; the highest (layer N) is the user interface.

• With modularity, layers are selected such that each uses functions (operations) and services of only lower-level layers.

UNIX System Structure

Process Management

• Process vs. Thread creation

• Process scheduling

• Process Termination

• Unix process creation fork() & exec()– Identify parent vs. child

• How to find out process infomation

Process Control Block (PCB)

Process vs. Thread creation

Multithreading Models

• Many-to-One

• One-to-One

• Many-to-Many

----------------------------------------------

• Pthread, JAVA thread, Kernel vs. User thread

CPU Switch From Process to Process

Process Scheduling Queues

• Job queue – set of all processes in the system.

• Ready queue – set of all processes residing in main memory, ready and waiting to execute.

• Device queues – set of processes waiting for an I/O device.

• Process migration between the various queues.

Representation of Process Scheduling

Schedulers

• Long-term scheduler (or job scheduler) – selects which processes should be brought into the ready queue.

• Short-term scheduler (or CPU scheduler) – selects which process should be executed next and allocates CPU.

• Midterm scheduler

Addition of Medium Term Scheduling

Scheduling Criteria

• CPU utilization – keep the CPU as busy as possible• Throughput – # of processes that complete their

execution per time unit• Turnaround time – amount of time to execute a particular

process (finishing time – arrival time)• Waiting time – amount of time a process has been

waiting in the ready queue• Response time – amount of time it takes from when a

request was submitted until the first response is produced, not output (for time-sharing environment)

Class Exercise

Process Timep1 6P2 3P3 7p4 1

Each team works on finding an average turnaround time for a quantum time at 1, 2, 3, 4, 5, 6, 7

First-Come, First-Served (FCFS) Scheduling

Process Burst Time

P1 24

P2 3

P3 3

• Suppose that the processes arrive in the order: P1 , P2 , P3

The Gantt Chart for the schedule is:

• Waiting time for P1 = 0; P2 = 24; P3 = 27

• Average waiting time: (0 + 24 + 27)/3 = 17

P1 P2 P3

24 27 300

Turnaround Time Varies With The Time Quantum

Context Switch

• When CPU switches to another process, the system must save the state of the old process and load the saved state for the new process.

• Context-switch time is overhead; the system does no useful work while switching.

• Time dependent on hardware support.

User program & Kernel interface

Note: This picture is excerpted from Write a Linux Hardware Device Driver, Andrew O’Shauqhnessy, Unix world

Two I/O Methods

Synchronous Asynchronous

Pooling or interrupt