Operating Systems

• Manage system resources– CPU scheduling– Process management– Memory management– Input/Output device management– Storage device management (hard disks,

CD/DVD drives, etc)– File System Management

• Simplify the development and use of applications

Purpose of an Operating System

• Microsoft Windows• MacOS• Mac and PCs are not directly

compatible but virtualization can be used.

Mainstream Operating Systems

• Operating system for large computers about 40 years ago.

• Linux– Free implementation of Unix– Supported by most platforms

UNIX

• Most “devices” use an operating system to make application development easier.

• Examples: – cell phones (Symbian, BlackBerry,

Windows Mobile, etc).– Aircraft Systems (VxWorks, pSOS, QNX)

Special Purpose OS

• Layers need to be concerned with layer below (and above)

• Layers are isolated from certain changes

Layers

Running Multiple

Operating Systems

Virtual Machine

Hardware

Windows (OS)

Windows Application VMWare Application

Linux (OS)

Linux Application

Running a Virtual

Machine

USER

Windows Applications

Windows

HARDWARE

Figure 2.3Layers with a virtual operating system

LinuxApplications

Linux

Virtual Computer Application

OS Modes

• A typical operating system has two modes of operation. – User Mode– Kernel Mode

• These are like layers of operation within the operating system layer.

User Mode

• The User Mode is concerned with the actual interface between the user and the system.

• It controls things like running applications and accessing files.

Kernel Mode

• The Kernel Mode is concerned with everything running in the background.

• It controls things like:– accessing system resources– controlling hardware functions– processing program instructions.

• The Kernel forms the core of the operating system.– acts like a supervisor for everything that is

happening in the computer.

The Client-Server OS Model

• In the client-server model of an operating system, the User Mode is considered a client.– the User Mode accesses resources

provided by the Kernel (the server).

Gra

ph

ics

Sys

tem

ApplicationService

Typical OS Architecture

ServiceService

Service

ApplicationApplication

Application

Application Interface

Sch

ed

ule

r

Me

mo

ry

Ma

na

ge

r

I/O

De

vice

M

an

ag

er

File

Sys

tem

Se

curit

y S

yste

mKernel

Hardware

User mode(client)

Kernel mode(server)

Gra

ph

ics

Sys

tem

Dispatcher

• Way for the user to control the operating system.

• Two types: graphical user interface (GUI) and command line interface

User Interface

Who starts the OS?

GUI & Command Line

Command Line Interpreter

• Converts typed commands into operating system actions (system calls).

• Most interpreters execute applications to perform the system calls.

Managing System Resources

• An operating system needs to manage a wide range of system resources:– CPU scheduling and process

management– Memory (RAM)– Access to peripheral devices– File system management.

• Decide when applications should run; does the order matter?

• Are the applications active or sleeping?

• Multiple applications at the same time

CPU Scheduling

Word

Applications

Microsoft Outlook

Adobe Acrobat

Internet Explorer

The Process Table

• Keeping track of all of the processes is done with the Process Table.

• The Process Table lists:– Processes that are currently being run– Processes that are waiting to be

executed– Processes that have been temporarily

suspended– It also keeps track of the current status,

or state, of each process.

• Give memory to each application as needed.

• Protect applications from each other

• Protect operating system from ‘bad’ applications

Memory Management

Windows

Word

Internet Explorer

Internet Explorer

Unused

RAM

• Devices are very difficult to program• OS Provides Drivers• Applications speak to drivers• Drivers communicate to device

Peripherals

• Manage Information (files and folders)

• Provide common view of storage devices

File System

Review Questions1. Describe two tasks that are performed by an

operating system.

2. Describe the four layers of interaction in an operating system model.

3. Briefly describe how you can install multiple operating systems on the same computer.

4. Draw a diagram to demonstrate how virtualization can be used to run multiple operating systems at the same time.

5. Briefly describe the client-server model of an operating system.

6. Draw a simple diagram to show the two modes of operations of an OS.

7. Briefly describe the function of the Command Line Interpreter.

8. What are the major differences between System Calls and Interrupts?

9. Describe the purpose of the Process Table.

Thank you