OPERATING SYSTEM:MS-DOS AND WINDOWS

Chapter 5

What is an OS?It is an extended machine (interface to the

machine)• Hides the messy details which must be performed• Presents user with a virtual machine, easier to use

It is a resource manager• Each program gets time with the resource• Each program gets space on the resource

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OS for 4th Generation ComputersPersonal computers

CP/M (Control Program for Microcomputers)

DOS (Disk Operating System) MS-DOS

GUI (Graphical User Interface)

Windows Windows 95/98/Me, Windows NT, Windows 2000, Windows XP

UNIX: X Windows, Motif

Linux, Gnome, KDE

Mainframe operating systems OS/390, OS/360

Server operating systems UNIX, Windows 2000/XP,

Linux

Multiprocessor operating systems Windows XP, Linux, Dynix

Real-time operating systems VxWorks, QNX

Embedded operating systems PalmOS, Pocket PC for

PDA, Windows Mobile, Symbian OS

Smart card operating systems Java Virtual Machine (JVM)

on the smart card

Functions of operating system1. Process management 2. Memory management3. File management4. Device management5. Security management6. User Interface (Command Interpretation)

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What is a process?A process is an execution of a program by the

processing unit.Several tasks of MS Word-

• editing the document• the user may start printing a spreadsheet • read data from CD-ROM

A process requires certain resources like CPU time allocation, memory space, files and I/O devices.

Managing the process assigned by the user and accomplishing all the tasks by making proper and efficient use of hardware resources.

What is process life-cycle?When there are processes running on a computer,

operating system allocates certain amount of time to each process for making use of the processor. So, the process may be at different stages of execution. These are - Running, ready and waiting.

Running – the process which is allowed by the operating system to use the processor.

Ready – the process which can run when the processor becomes free.

Waiting – the running process which is interrupted after completing its allotted time and kept waiting (to be processed later).

The change of the state from one to another is known as context change and the action is known as context switching.

What is process scheduling? In a multiprogramming environment the processor is

required to handle many processes at a given time and these processes are to be the processor time, which is known as scheduling.

Two most popular implementation of scheduling are – First in First out (FIFO) and Round Robin

First in First out and (FIFO) – In this system, all the available processes are kept in queue. When the first one is dispatched to the processor all other processes move up one slot in the queue. In this approach, a process may take up long time to complete and holds up other processes in the queue.

Round Robin – In this approach, a process is allowed to run for a fixed period of time known as time slicing, after which it is interrupted and sent to the end of the queue.

Queues at process

Characterization of Scheduling PoliciesThe scheduler (scheduling procedure)

determines which ready process is selected next for execution

The decision mode specifies the instants in time the selection function is exercised

• Once a process is in the running state, it will continue until it terminates or blocks for an I/O

Nonpreemptive

• Currently running process may be interrupted and moved to the Ready state by the OS

• Prevents one process from monopolizing the processor

Preemptive

First Come First Served (FCFS)Selection function: the process that has

been waiting the longest in the ready queue (hence, FCFS)

Decision mode: non-preemptivea process runs until it blocks for an I/O

Favors CPU-bound processesA CPU-bound process monopolizes the processorI/O-bound processes have to wait until completion of CPU-bound process

I/O-bound processes may have to wait even after their I/Os are completed (poor device utilization)

Better I/O device utilization could be achieved if I/O bound processes had higher priority

Round-Robin

Decision mode: preemptivea process is allowed to run until the time slice period (quantum, typically from 10 to 100 ms) has expireda clock interrupt occurs and the running process is put on the ready queue

Still favor CPU-bound processesAn I/O bound process uses the CPU for a time less than the time quantum before it is blocked waiting for an I/OA CPU-bound process runs for all its time slice and is put back into the ready queue

May unfairly get in front of blocked processes

DeadlockProcess is deadlocked if it is waiting for an

event that will never occurMost common situation is where two processes

are involved on is holding resource required by the other and also looking for resource held by the other process.

Alamgir locks AB123Bibi Russel lock AB456

Alamgir requests AB456Bibi Russel requests AB123

Deadlock prevention means that deadlock will not occur due to fact that we deny one of the 4 conditions necessary.

Deadlock avoidance attempts to predict the possibility of deadlock as each resources request is made.

Example if process A requests a resource held by process B then make sure that process B is not waiting for resource held by A (Banker’s algorithm)

Memory ManagementPart of the operating system

that manages the memory of a computer is known as memory manager.

Two major tasks are involved in memory management: • allocation of memory space

to each process; and • effective utilization of

different types of memory.

Memory protectionEnsures that that memory location allocated to one process is not being used by any other process. The operating system keeps track of the memory space assigned to each program.

Virtual memoryVirtual memory acts like a main memory to the user, although it is no real memory. A part of the secondary storage device (like hard disk) is linked with the main memory through the referenced page pf a program and made available to the user, when necessary.

File ManagementIt may also be described as information management

because information• is stored in the system in the form of files. Process can read

information• from files and can create new files for newly generated

information.

File manager of the operating system is responsible for maintenance of the file system;

• providing directories for organizing files; and • providing a protection mechanism to allow different users to

access information stored in different files.

Device ManagementDevice management module of an operating system

controls all the I/O devices of a computer. For example, a printer is recognized and used through the operating system.

Objective• keeps track of I/O requests from processor• Issue command to the I/O devices • Ensure correct data transmission to and from I/O

devices.SPOOLINGSPOOL stands for Simultaneous Peripheral Operation On-line. It refers to putting jobs in a buffer memory where a device can access them when it is ready. The processor send the data very fast and the buffer provides a waiting space while the slower device catches up. The most common spooling application is print spooling.

Security ManagementThis module of operating system provides

protection against data corruption (or destruction) and unauthorized access.

Two major security techniques are:• data backup and • user authentication (like the use of password)

User InterfaceCommand interpretation module (also known as

command interpreter) of an operating system serves as an interface for the user to communicate with the computer via its operating system.

Two types of interface may be provided to the user. (i) Command Line Interface (CLI) – Here the user gives

user to the computer by typing commands line by line. DOS and UNIX are the examples of the operating system providing CLI.

(ii) Graphical User Interface (GUI) – Here the command is graphical or pictorial. User can give commands by clicking icons and opening dialog boxes. Commands are selected by moving a pointer (generally by using mouse). WINDOWS and LINUX are the examples of GUI based operating systems.

UtilitiesUtility programs- Assist the

users with the system maintenance tasks.

Common utilities • Disk formatting • Disk compaction • Disk cleanup• Data compression• Data backup • Data recovery • Virus protection • Firewall

• Performance Monitoring/ Profiler- Analyzing the performance of • various hardware

components • overall performance of a

computer system.

• Information • % of CPU utilization• % of memory

utilization• number of disk

accesses

Common DOS commandsdir [name of directory]

dir allows you to list all contents of the specified directory

Mkdir- Make directorycd <directory name>

cd is the basic DOS command, it allows you to change directory

copy <source> <destination> Allows you to copy a

file from a <source> folder to a <destination folder>

del<file> Deletes a specific file

move <source> <destination> Allows you to move a

file from a <source> folder to a <destination folder>

ren <source> <destination> Renames the specified

file exit

Leaves the DOS terminal

Common DOS commands …edit <filename>

Opens the default DOS editor to allow modification of a specified file

cls Clears the DOS screen

AssignmentsIOA, IA, GA, Case !@#$