Lecture Notes

Operating Systems

Dr. Ming Zhang

Tel: +1 (757) 594 7065 Fax: +1 (757) 594 7919

Office: Gosnold Hall 223 Email: mzhang@pcs.cnu.edu

URL: http://www.pcs.cnu.edu/~mzhang http://www.DrMingZhang.com

http://j2ee.pcs.cnu.edu/moodle

Operating Systems Subject Introduction Dr. Ming Zhang

Contents of Operation Systems (1)* Operation System* Processes * Concurrency& UNIX Concurrency Mechanisms* Memory

- Memory Management - Virtual Memory* Scheduling - Uniprocessor Scheduling - Multiprocessor Scheduling * Input/Output and Files* Distributed Systems (CPSC 450)* Security(CPSC 450)Network Programming Overview Dr. Ming Zhang

Contents of Operation Systems (2)

* Processes • Process Description• Process Environment• Process Control• Threads• SMP (symmetric Multiprocessing)• Microkernel

Operating Systems Subject Introduction Dr. Ming Zhang

Contents of Operation Systems (3)

* Concurrency• Mutual Exclusion • Synchronization• Dead Lock • Starvation

Operating Systems Subject Introduction Dr. Ming Zhang

Contents of Operation Systems (4)* Memory Management

buddy SystemPaging

* Scheduling (Uniprocessor Scheduling)First-Come-First-Served (FCFS)Round-Robin (RR): q=1; q=4Shortest Process Next (SPN)Shortest Remaining Time (SRT)Highest Response Ratio Next (HRRN)Feedback q=1; q=2i

* Input/Output and FilesDisk SchedulingFire Organization

Network Programming Overview Dr. Ming Zhang

Prescribed Text

William StallingOperating Systems - Internal and Design Principles2005, Fifth EditionPrentice HallINSB: 0 - 13 - 147954Winner of the 1998 text award for the best

computer science and engineering textbook

Operating Systems Subject Introduction Dr. Ming Zhang

Exercises/Homework

Exercise/Homework

Operating Systems Subject Introduction Dr. Ming Zhang

Tests

* Test 1:

* Test 2:

* Test 3:

Operating Systems Subject Introduction Dr. Ming Zhang

Project: Construction of a Larger System

Programming: 2,000 -3,000 LinesProject Report: 3,000 wordsOral Presentation: 5 minutes per

person

Operating Systems Subject Introduction Dr. Ming Zhang

Final Examination

* Time 2.5 hours

Operating Systems Subject Introduction Dr. Ming Zhang

Operating Systems History

Operating systemsSubroutineBatch monitorBuffering and interruptMultiprogramming Interactive timesharingPreemptive schedulingDistributed operating systemsNetwork and Computer Security

Operating System

A program that controls the execution of application programs

An interface between the user and hardware

Masks the details of the hardware

What is an operating system?

Hard to define preciselybecause operating systems arose historically as people needed to solve problems associated with using computers.

In the beginning: Expensive Hardware, Cheap People

Goal: maximize hardware, utilization. Now: Cheap Hardware, Expensive People

Goal: make it easy for people to use computer

Layers and Views of a Computer System

EndUser

Programmer

Operating-System

Designer

Computer Hardware

Operating-System

Utilities

ApplicationPrograms

Problem: code to manipulate external I/O devices

Solution:Build a subroutine library (device drivers) to

manage the interaction with the I/O devices. The library is loaded into the top of memory

and stays there. This is the first example of something that

would grow into an operating system. Because the machine is so expensive, it is

important to keep it busy.

Services Provided by the Operating System

Program creation editors and debuggers

Program executionAccess to I/O devicesControlled access to filesSystem access

Services Provided by the Operating System

Error detection and response internal and external hardware errors

memory errordevice failure

software errorsarithmetic overflowaccess forbidden memory locations

operating system cannot grant request of application

Accounting collect statistics monitor performance used for billing users

Services Provided by the Operating System

Operating System

It is actually a programDirects the processor in the use of

system resourcesDirects the processor when

executing other programsProcessor stops executing the

operating system in order to execute other programs

Operating System as a Resource Manager

Processor . . .

.

.

.

Computer System

I/O Controller

Processor

I/O Controller

I/O Controller

Memory

OperatingSystemSoftware

Programsand Data

O/SPrograms

Data

Problem: computer idles while programmer sets things up

Solution:Build a batch monitor. Store jobs on a disk (spooling), have

computer read them in one at a time and execute them.

Big change in computer usage: debugging now done offline from print

outs and memory dumps. No more instant feedback.

Monitors

Software that controls the running programs

Batch operating systemJobs are batched togetherResident monitor is in main memory

and available for executionMonitor utilities are loaded when

needed

Memory Layout For a Resident Monitor

Boundary

InterruptProcessing

DeviceDrivers

JobSequencing

Control LanguageInterpreter

UserProgram

Area

Monitor

Problem: At any given time, job is actively using either the CPU or an I/O device, and the rest of the machine is idle and therefore unutilized

Solution: Allow the job to overlap computation and

I/O. Buffering and interrupt handling added to subroutine library.

Hardware Features

Memory protection do not allow the memory area

containing the monitor to be alteredTimer

prevents a job from monopolizing the system

an interrupt occurs when time expires

Hardware Features

Privileged instructions executed only by the monitor an interrupt occurs if a program tries

these instructionsInterrupts

provides flexibility for controlling user programs

Problem: one job can't keep both CPU and I/O devices busy. Get poor utilization either of CPU or I/O devices.

Solution: multiprogramming - several jobs share

system. Dynamically switch from one job to another when the running job does I/O.

Allows the processor to execute another program while one program must wait for an I/O device.

Run RunWait

Time

Wait

RunA

RunAWait

Time

WaitRunB

RunB

Multiprogramming or Multitasking

Example

JOB1 JOB2 JOB3

Type of job Heavy compute Heavy I/O Heavy I/O

Duration 5 min. 15 min. 10 min.

Memory required 50K 100 K 80 K

Need disk? No No Yes

Need terminal No Yes No

Need printer? No No Yes

Effects of Multiprogramming

Uniprogramming Multiprogramming

Processor use 17% 33%

Memory use 30% 67%

Disk use 33% 67%

Printer use 33% 67%

Throughput rate 6 jobs/hr 12 jobs/hr

Mean response time 18 min. 10 min.

Big issue: protection

Don't want one job to affect the results of another.

Memory protection and relocation added to hardware, OS must manage new hardware functionality.

OS starts to become a significant software system.

OS also starts to take up significant resources on its own.

Phase shift: Computers become much cheaper.People costs become significant.

Issue: It becomes important to make computers easier to use and to improve the productivity of the people.

Problem: having to wait for batch output . So, it is important to run interactively. But computers are still so expensive that you can't buy one for every person.

Solution: interactive timesharing.

Time Sharing

Using multiprogramming to handle multiple interactive jobs

Processor’s time is shared among multiple users

Multiple users simultaneously access the system through terminals

Problem: Old batch schedulers were designed to run a job for as long as it was utilizing the CPU effectively. But now, people need reasonable response time from the computer. Solution: Preemptive scheduling.

Scheduling and Resource Management

Fairness give equal and fair access to all processes

Differential responsiveness discriminate between different classes of

jobsEfficiency

maximize throughput, minimize response time, and accommodate as many uses as possible

Phase shift:Computers become even cheaper. It becomes practical to give one computer to each user.

Issue:OS resource consumption becomes a

big issue

Problem:People need to share data and information with other people

Solution: Networking, distributed operating

systems and modern operating systems

Problem:Networking becomes very important, and as sharing becomes an important part of the experience

Issue:Network securityComputer security

The major problem facing computer science today is how to build large, reliable software systems. Operating systems are one of very

few examples of existing large software systems.

By studying operating systems, we may learn lessons applicable to the construction of larger systems.