operating system: ms-dos and windows chapter 5. what is an os? it is an extended machine (interface...
TRANSCRIPT
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
3
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 system
1. Process management 2. Memory management3. File management4. Device management5. Security management6. User Interface (Command Interpretation)
5
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
• 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 processes
A CPU-bound process monopolizes the processor
I/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 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 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 Management
Part 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 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.
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 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.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 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 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
AssignmentsIOA, IA, GA, Case !@#$