Chapter 5
OPERATING SYSTEM:
MS-DOS AND WINDOWS
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
OS for 4th Generation Computers
Personal
computers
Mainframe
operating
systems
CP/M (Control
Program for
Microcomputers)
Server
operating
systems
DOS (Disk
Operating
System)  MSDOS
OS/390, OS/360
UNIX, Windows 2000/XP,
Linux
Multiprocessor
operating
systems
Windows XP, Linux, Dynix
Real-time
operating
systems
VxWorks, QNX
GUI (Graphical
User Interface)
Windows
UNIX:
Windows
95/98/Me,
Windows NT,
Windows 2000,
Windows XP
X Windows, Motif
Linux, Gnome, KDE
Embedded
operating
systems
Smart card
operating
systems
PalmOS, Pocket PC for PDA,
Windows Mobile, Symbian OS
Java Virtual Machine (JVM) on
the smart card
Functions of operating system
1.
2.
3.
4.
5.
6.
Process management
Memory management
File management
Device management
Security management
User Interface (Command Interpretation)
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 Policies
The 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
Nonpreemptive
• Once a process is in the running state, it will continue until it
terminates or blocks for an I/O
Preemptive
• Currently running process may be interrupted and moved to
the Ready state by the OS
• Prevents one process from monopolizing the processor
First Come First Served (FCFS)
Selection function: the process that has been waiting
the longest in the ready queue (hence, FCFS)
Decision mode: non-preemptive
a process runs until it blocks for an I/O
Favors CPU-bound processes
A CPU-bound process monopolizes the processor
I/O-bound processes have to wait until completion of CPUbound 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: preemptive
a process is allowed to run until the time slice period
(quantum, typically from 10 to 100 ms) has expired
a clock interrupt occurs and the running process is put on the
ready queue
Still favor CPU-bound processes
An I/O bound process uses the CPU for a time less than the time
quantum before it is blocked waiting for an I/O
A 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
Deadlock
Process is deadlocked if it is waiting for an event that
will never occur
Most 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 AB123
Bibi Russel lock AB456
Alamgir requests AB456
Bibi 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 Management
Part of the operating system that
manages the memory of a
computer is known as
memory manager.
Memory protection
Ensures 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.
Two major tasks are involved in
memory management:
• allocation of memory space to
each process; and
• effective utilization of different
types of memory.
Virtual memory
Virtual 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 Management
It 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 Management
Device 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.
•
•
•
SPOOLING
SPOOL 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 Management
This 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 Interface
Command 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.
Utilities
Utility 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 commands
dir [name of directory]
dir allows you to list all
contents of the specified
directory
Mkdir- Make directory
cd <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
Assignments
IOA, IA, GA, Case !@#$