Operating system 3

CECOS DATA INSTITUTE
Operating System
WINDOWS 7 & LINUX
Prepare by: Mohsin Khan
You can contact me with the following links
Cell: 0336-9759874
Skype: MOHSIN.KHAN1341

Operating System
April 1, 2014
PREPARE BY: MOHSIN KHAN FACE BOOK: MODERN.MOHSIN
1
OPERATING SYSTEM
Operating System can be defined as below;
 “An operating system is system software that manages all the resources of a computer system”
 “An Operating system is a program that manages computer hardware”
 “An operating system is a group of computer programs that coordinates all
the activities among computer hardware devices, It is the first program
loaded into the computer by a boot program and remains in memory at all
times”
FUNCTIONS OF OPERATING SYSTEM
The Operating System provides following functions:
 Booting the computer
 Provides a user interface
 Handles system resources
 Provides file management
 Multiprogramming
 Multitasking
 Multiprocessing
 Multithreading
I. BOOTING THE COMPUTER
“The process of starting or restarting the computer is known as booting. A
cold boot is when you turn on a computer that has been turned off completely. A
warm boot is the process of using the operating system to restart the computer”
II. PROVIDES USER INTERFACE
A user interacts with software through the user interface. The two main types of
user interfaces are: command line and a graphical user interface (GUI).
 Disk Operating System (DOS): With a command line interface, the user
interacts with the operating system by typing commands to perform specific
tasks. An example of a command line interface is DOS (disk operating
system).
 Graphical User Interface (GUI): With a graphical user interface, the user
interacts with the operating system by using a mouse to access windows,
icons, and menus. An example of a graphical user interface is Windows Vista
or Windows 7.
III. HANDLES SYSTEM RESOURCES
The operating system also handles system resources such as the computer's memory
and sharing of the central processing unit (CPU) time by various applications or
peripheral devices.

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IV. PROVIDES FILE MANAGEMENT
The file management system allows the user to perform such tasks as creating files
and directories, renaming files, coping and moving files, and deleting files. The
operating system keeps track of where files are located on the hard drive through
the type of file system. The type two main types of file system are File Allocation
table (FAT) or New Technology File system (NTFS).
V. MULTIPROGRAMMING
In multiprogramming the operating system executes part of one program, then part
of another, and so on. To the user it appears that all programs are executing at the
same time. If a process needs an IO only then that process is sent to waiting queue
and other process gets the attention of the CPU
VI. MULTITASKING
Multitasking is the extension of multiprogramming. The concept of time sharing was
implemented in multitasking. So that all the process gets the attention of processor,
Different scheduling algorithms are used to implement multitasking.
VII. MULTIPROCESSING
Multiprocessor systems (also known as parallel systems or multi core systems)
Such systems have two or more processors in close communication, sharing the
computer bus and sometimes the clock, memory, and peripheral devices.
The multiple-processor systems in use today are of two types. Some systems use
asymmetric multiprocessing, in which each processor is assigned a specific task. A
boss processor controls the system; the other processors either look to the boss for
instruction or have predefined tasks. This scheme defines a boss–worker
relationship. The boss processor schedules and allocates work to the worker
processors.
The most common systems use symmetric multiprocessing (SMP), in which each
processor performs all tasks within the operating system. SMP means that all
processors are peers; no boss–worker relationship exists between processors.

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April 1, 2014
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Major Part of Operating System
The OS can be broken down into four main parts,
1. Kernel
2. Device Drivers
3. User Interface
4. System Utilities
1) KERNEL
This has the task of loading the applications into memory, making sure they do not interfere with
one another and allowing them to share use of the CPU efficiently. The kernel also handles file storage to
and from secondary storage devices such as hard disks and optical drives.
In other words the kernel handles:
 Loading / unloading applications from memory
 Scheduling tasks to run on the CPU
 Memory management
 File management
 Data security
2) DEVICE DRIVERS
More commonly known as a driver, a device driver is a group of files that enable one or
more hardware devices to communicate with the computer's operating system. Without drivers, a
hardware device such as a computer printer would not be able to work with the computer.
3) USER INTERFACE
Alternatively referred to as a human-computer interface, a user interface is the portion of a software
program or hardware device that is used to navigate and control aspects of the software program or
hardware device.
4) SYSTEM UTILITIES
This part of operating system provides all basic facilities that run in background without user interaction.
For example,
 Print Spool Services
 Cryptographic password management
 File management services

Operating System
April 1, 2014
4
Types of operating system
I. SINGLE-USER, SINGLE TASK: As the name implies, this operating system is designed to
manage the computer so that one user can effectively do one thing at a time. The Palm
OS for Palm handheld computers is a good example of a modern single-user, single-task
operating system.
II. SINGLE-USER, MULTI-TASKING: This is the type of operating system most people use on their
desktop and laptop computers today. Microsoft's Windows and Apple's Mac-OS platforms
are both examples of operating systems that will let a single user have several programs
in operation at the same time. For example, it's entirely possible for a Windows user to be
writing a note in a word processor while downloading a file from the Internet while printing
the text of an e-mail message.
III. MULTI-USER: A MULTI: user operating system allows many different users to take advantage
of the computer's resources simultaneously. The operating system must make sure that
the requirements of the various users are balanced, and that each of the programs they
are using has sufficient and separate resources so that a problem with one user doesn't
affect the entire community of users. UNIX, VMS and mainframe operating systems, such
as MVS, are examples of multi-user operating systems.
Scheduling
 “Scheduling is the job of allocating CPU time to different tasks within an operating system”
 “Select from among the processes in memory that are ready to execute, and allocates the CPU to
one of them”
Types of Scheduling
In general, there are two types of scheduling: In general, there are two types of scheduling: non-
preemptive scheduling, and preemptive scheduling.
 In non-preemptive scheduling, a process runs until it terminates stops, blocks, suspends,
or yields.
 In preemptive scheduling, even if the current thread is still running, a context switch will
occur when its time slice is used up. Or (An interrupt causing currently running program
to give up the CPU and be replaced by another process)

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April 1, 2014
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Scheduling Algorithm
FIRST-COME, FIRST SERVE (FCFS):
FCFS also called FIFO (First-in, first-out)
Simple, fair, but poor performance, the average waiting time will be long. The process
that comes last, have to wait longer.
The algorithm simply schedules the jobs in the order in which they arrive, and runs each
one to completion.
EXAMPLE DATA:
Process Arrival Time Service
Time
1 0 8
2 1 4
3 2 9
4 3 5
FCFS IS APPLIED THEN THE PROCESSES WILL EXECUTE IN FOLLOWING FASHION.
SHORTEST JOB FIRST (SJF):
A different approach to CPU scheduling is the shortest-job-first (SJF) scheduling
algorithm. When the CPU is available, it is assigned to the process that has the smallest
next CPU process. Moving a short process before long one decrease the waiting time of
the short process more than it increases the waiting time of the long process.
Time
1 0 8
2 1 4
3 2 9
4 3 5

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April 1, 2014
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SJF IS APPLIED THEN THE PROCESSES WILL EXECUTE IN FOLLOWING FASHION.
ROUND ROBIN (RR):
The round-robin (RR) scheduling algorithm is designed especially for time-sharing
systems. A small unit of time, called a time quantum or time slice, is defined. A time
quantum is generally from 10 to 100 milliseconds.
Example Data:
Time
1 0 8
2 1 4
3 2 9
4 3 5
RR IS APPLIED THEN THE PROCESSES WILL EXECUTE IN FOLLOWING FASHION.

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April 1, 2014
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Deadlock
Deadlock is defined as the permanent blocking of a set of processes that compete for
system resources.
In a multiprogramming environment, several processes may compete for a finite
number of resources.
A process requests resources; and if the resources are not available at that time, the
process enters a waiting state. Sometimes, a waiting process is never again able to
change state, because the resources it has requested are held by other waiting
processes.
NECESSARY CONDITIONS
A deadlock situation can arise if the following four conditions hold simultaneously in a
system:
Mutual exclusion
At least one resource must be held in a non-sharable mode;
That is, only one process at a time can use the resource.
If another process requests that resource, the requesting process must be delayed until
the resource has been released.
Hold and wait A process must be holding at least one resource and waiting to acquire
additional resources that are currently being held by other processes.
No preemption Resources cannot be preempted, that is, a resource can be released
only voluntarily by the process holding it, after that process has completed its task.
Circular wait A set of waiting processes must exist such that is
waiting for a resource held by , is waiting for a resource held by is
waiting for a resource held by , is waiting for a resource held by .There must
be a circular chain of two or more processes, each of which is waiting for a resource
held by the next member of the chain.

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Methods for Handling Deadlocks
Generally speaking, we can deal with the deadlock problem in one of three ways:
1. We can use a protocol to prevent or avoid deadlocks, ensuring that the
system will never enter a deadlock state.
o To ensure that deadlocks never occur, the system can use either a
deadlock-prevention or a deadlock-avoidance scheme.
o Deadlock prevention provides a set of methods for ensuring that at
least one of the necessary conditions cannot hold.
o Design a system in such a way that the possibility of deadlock is
excluded a priori (compile-time/statically, by design).
o Deadlock avoidance requires that the OS be given in
advance additional information concerning which resources a
process will request and use during its lifetime. With this
additional knowledge, it can decide for each request whether or
not the process should wait.
o Make a decision dynamically checking whether the request will, if
granted, potentially lead to a deadlock or not. (run-
time/dynamically, before it happens).
2. We can allow the system to enter a deadlock state, detect it, and recover.
o If a system does not employ either a deadlock-prevention or a
deadlock-avoidance algorithm, then a deadlock situation may
arise.
o In this environment, the system can provide an algorithm that
examines the state of the system to determine whether a
deadlock has occurred and an algorithm to recover from the
deadlock.
o Let deadlocks occur, detect them, and take action (run-
time/dynamically, after it happens)
3. We can ignore (The Ostrich Algorithm; maybe if you ignore it, it will
ignore you) the problem altogether and pretend that deadlocks never
occur in the system.
o If a system neither ensures that a deadlock will never occur nor
provides a mechanism for deadlock detection and recovery, then

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April 1, 2014
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we may arrive at a situation where the system is in a deadlocked
state yet has no way of recognizing what has happened.
o Eventually, the system will stop functioning and will need to be
restarted manually.
o In many systems, deadlocks occur infrequently (say, once per
year); thus, this method is cheaper than the prevention, avoidance,
or detection and recovery methods.

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April 1, 2014
10
INSTALLING WINDOWS 7
Windows 7 Hardware Requirements
The Windows 7 Minimum hardware requirements are as follows:
 At least 800MHz 32-bit (x86) or 64-bit (x64) processor
 512MB of RAM
 A video card capable of at least 800×600 resolution and DirectX 9 with at least 32MB of
graphics RAM
 A DVD drive
 Audio output capability
 A hard drive that is at least 40GB in total size, with at least 16GB of free space
By comparison, here are the Windows 7 Recommended specifications:
 A 1GHz (or faster) 32-bit (x86) or 64-bit (x64) processor
 A minimum of 1GB of RAM
 A video card that supports DirectX 9 graphics with a WDDM driver and has at least
128MB of
 graphics memory
 Video card support for Pixel Shadier 2.0 and 32 bits per pixel
 A hard drive that is at least 80GB in total size, with at least 40GB of free space
 A DVD drive
 Audio output capability
 Internet connectivity for product activation
Steps for Installation
 Turn your computer on then press Del or F2 (depend on your computer’s mainboard) to
enter the system BIOS
 Go to Boot menu and choose Boot from CD/DVD.
 Press F10 to save the configuration and exit BIOS then reset your computer.
 Insert Windows 7 DVD into your DVD drive then start up your computer, Windows 7 will
be loading files.
 Language to Install, Time and currency format, Keyboard or input method. Then click
NEXT.
 Choose the Windows 7 version that you want to install in 'Select the operating system
you want to install’. Here we choose Windows 7 Ultimate then click next (depending on
your Windows DVD, this step is an option).
 Click 'I accept the license terms' in 'Please read the license' then click NEXT.
 Choose 'Upgrade' in 'Which type of installation do you want' if you want to upgrade from
an older Windows version to Windows 7, 'Custom (advance)' if you want to install a new
version of Windows.
 Choose Partition for installation, if your computer has only one hard disk, it will be easy
for selection, but if it has some Partition, you will have to consider which Partition to
choose.
 Your computer might be restarted during the process.
 Type you’re a user account and computer name. After click NEXT.
 Type a password for your account, you can also Type a password hint to help in case of
forgetting the password in the future, and then click NEXT.

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 Type in activation code or key for your license in Product key box if you have any. Click
NEXT.
 Choose how to protect your Windows. Here we choose Use recommended settings.
 Set up your Time zone then click NEXT.
 Public Network, Work Network, Home Network. Choose Home Network for using Internet
at home.
Released Date of
windows 7:
I Was Released on 22nd July,
2009
MAIN EDITIONS
Windows 7
Starter
Windows 7 Home
Basic
Windows 7 Home
Premium
Windows 7
Professional
Windows 7
Enterprise
Windows 7 Ultimate

Operating system 3

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