Introduction to Operating System

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Re: Introduction to Operating System

Unread postby Aoun Raza » Mon Apr 20, 2015 9:05 pm

Operating System

 OS is an integrated set of programs used to manage the computer resources and its overall operations.
 Provide a layer of services which manage the resources of the hardware and permit the user to drive the system.
 OS is a control programs which manages computer resources and allocate these resources among competing tasks.
 OS control and coordinates use of hardware among applications for users.
 OS is the interface between the hardware and software environment.
 OS is a program that acts as an intermediary between the user and computer hardware.

Goals of Operating System

 User Oriented
o Execute user programs and make solving user problems easier.
o Operating system should be convenient to use, easy to learn, reliable, safe, and fast.
 System Oriented
o Operating system should be easy to design, implement, and maintain, as well as flexible, reliable, error-free, and efficient.
o Use the computer hardware in an efficient manner.

 An operating system performs
o Resource Management
 Process management
 Input and Output management
 Memory management
 Secondary storage management
 File System Management
o Resource Sharing
 Among Users
 Among CPUs
o Interfacing between hardware and users

Implementation of Operating System

 Traditionally written in assembly language, operating systems can now be written in higher-level languages like C or C++.
 An operating system is far easier to port (move to some other hardware) if it is written in a high-level language.
 Code written in a high-level language:
o can be written faster
o is more compact
o is easier to understand and debug

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Re: Introduction to Operating System

Unread postby Ehtesham Saeed » Mon Apr 20, 2015 9:07 pm

Operating System
First of all there are two types of software
• Application Software
• System software
OS (operating system) is also called system software. It means that all application software’s are dependent on operating system or system software.
In early time computers are built for the basic operations like ADD , SUB , etc but when operating system take part in the computer history, then computer makes our life easier then easier.
It is the type of software but without it computer hardware can’t works because every command of user which drives the computer hardware first goes to the operating system or system software then it drives the hardware according to the command or input.
Operating system that in which way it works.
We give input to the computer system 1st it goes to the operating system then it gives it to the disk drive or any application as shown in the figure. According it mouse and keyboard are the input devices and monitor and printer are the output devices
There are many types of operating system
1. MS windows
2. Android
3. Linux
4. Ubuntu etc
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Re: Introduction to Operating System

Unread postby saad raza » Mon Apr 20, 2015 9:09 pm

Introduction to operating system:
A working framework (Operating System) is the product segment of a PC framework that is in charge of the administration and coordination of exercises and the imparting of the assets of the PC. The OS goes about as a host for application programs that are run on the machine. As a host, one of the reasons of an OS is to handle the subtle elements of the operation of the equipment. All have the advantages and disadvantages, but they are all based on the same concepts.
In our computers every operating system has five central controller that’s work together in the form of team.
1.Memory manager.
2.Process manager
3.Device manager
4.Network manager
The memory manager is the head of the main memory, it checks every request from the memory and utilize if it is valid or not, it allows the location of the memory space which is not to allowed, it can also reallocate the free space for our request.
The manager which allocate the brain of the computer which ic called CPU (central processing unit) it process the job which is under the execution in the system.It is necessary to the process manager to track each of the spaders process and to handle the system which are associate to this job.
It monitor every devices, channel and control unit which are connected to the computer it has to choose the most efficient weight which allocate in the system, USB , printers , Hard devices e.t.c are the example of the device managers.
The file managers checks every type of file that is in the system such as txt files and stored applications .it also give the permission so the user can operate the required file. it tells us the file is read only or read or write only.
These allows the user to share the information of hardware and software resources.
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Re: Introduction to Operating System

Unread postby sufyan9458 » Tue Apr 21, 2015 7:55 am

Name sufyan khan
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Introduction of operating system
An operating system (OS) is the software component of a computer system that is responsible for the management and coordination of activities and the sharing of the resources of the computer. The OS acts as a host for application programs that are run on the machine. As a host, one of the purposes of an OS is to handle the details of the operation of the hardware. This relieves application programs from having to manage these details and makes it easier to write applications. Almost all computers use an OS of some type.
OSs offer a number of services to application programs and users. Applications access these services through application programming interfaces (APIs) or system calls. By using these interfaces, the application can request a service from the OS, pass parameters, and receive the results of the operation. Users may also interact with the OS by typing commands or using a graphical user interface

Operating system definition
An operating system is the most important software that runs on a computer. It manages the computer's memory, processes, and all of its software and hardware. It also allows you to communicate with the computer without knowing how to speak the computer's language. Without an operating system, a computer is useless.

Basic Operating System Concepts
The operating system must fulfill two main objectives:
Interact with the Each computer system includes a basic set of programs called the operating system. The most important program in the set is called the kernel. It is loaded into RAM when the system boots and contains many critical procedures that are needed for the system to operate. The other programs are less crucial utilities; they can provide a wide variety of interactive experiences for the user as well as doing all the jobs the user bought the computer for—but the essential shape and capabilities of the system are determined by the kernel. The kernel provides key facilities to everything else on the system and determines many of the
characteristics of higher software. Hence, we often use the term "operating system" as a synonym for "kernel."To enforce this mechanism, modern operating systems rely on the availability of specific hardware features that forbid user programs to directly interact with low-level hardware components or to access arbitrary memory locations. In particular, the hardware introduces at least two different execution modes for the CPU: a nonprivileged mode for user programs and a privileged mode for the kernel. Unix calls these User Mode andKernel Mode , respectively.

Multiuser systems
A multiuser system is a computer that is able to concurrently and independently execute several applications belonging to two or more users. Concurrently means that applications can be active at the same time and contend for the various resources such as CPU, memory, hard disks, and so on. Independently means that each application can perform its task with no concern for what the applications of the other users are doing. Switching from one application to another, of course, slows down each of them and affects the response time seen by the users.
User and groups
In a multiuser system, each user has a private space on the machine; typically, he owns some quota of the disk space to store files, receives private mail messages, and so on. The operating system must ensure that the private portion of a user space is visible only to its owner. In particular, it must ensure that no user can exploit a system application for the purpose of violating the private space of another user.
All users are identified by a unique number called the User ID, or UID. Usually only a restricted number of persons are allowed to make use of a computer system. When one of these users starts a working session, the system asks for a login name and a password. If the user does not input a valid pair, the system denies access. Because the password is assumed to be secret, the user's privacy is ensured.
To selectively share material with other users, each user is a member of one or more user groups , which are identified by a unique number called a user group ID . Each file is associated with exactly one group. For example, access can be set so the user owning the file has read and write privileges, the group has read-only privileges, and other users on the system are denied access to the file.

All operating systems use one fundamental abstraction: the process. A process can be defined either as "an instance of a program in execution" or as the "execution context" of a running program. In traditional operating systems, a process executes a single sequence of instructions in an address space; the address space is the set of memory addresses that the process is allowed to reference. Modern operating systems allow processes with multiple execution flows — that is, multiple sequences of instructions executed in the same address space.
Multiuser systems must enforce an execution environment in which several processes can be active concurrently and contend for system resources, mainly the CPU. Systems that allow concurrent active processes are said to bemulti programming or multiprocessing .It is important to distinguish programs from processes; several processes can execute the same program concurrently, while the same process can execute several programs sequentially.
On uni processor systems, just one process can hold the CPU, and hence just one execution flow can progress at a time. In general, the number of CPUs is always restricted, and therefore only a few processes can progress at once. An operating system component called the scheduler chooses the process that can progress. Some operating systems allow only nonpreemptable processes, which means that the scheduler is invoked only when a process voluntarily relinquishes the CPU. But processes of a multiuser system must be preemptable; the operating system tracks how long each process holds the CPU and periodically activates the scheduler.
Unix is a multiprocessing operating system with preemptable processes . Even when no user is logged in and no application is running, several system processes monitor the peripheral devices. In particular, several processes listen at the system terminals waiting for user logins. When a user inputs a login name, the listening process runs a program that validates the user password. If the user identity is acknowledged, the process creates another process that runs a shell into which commands are entered.

Kernel Architecture
As stated before, most Unix kernels are monolithic: each kernel layer is integrated into the whole kernel program and runs in Kernel Mode on behalf of the current process. In contrast, microkernel operating systems demand a very small set of functions from the kernel, generally including a few synchronization primitives, a simple scheduler, and an interprocess communication mechanism. Several system processes that run on top of the microkernel implement other operating system-layer functions, like memory allocators, device drivers, and system call handlers.
Although academic research on operating systems is oriented toward microkernels , such operating systems are generally slower than monolithic ones, because the explicit message passing between the different layers of the operating system has a cost. However, microkernel operating systems might have some theoretical advantages over monolithic ones. Microkernels force the system programmers to adopt a modularized approach, because each operating system layer is a relatively independent program that must interact with the other layers through well-defined and clean software interfaces.
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Re: Introduction to Operating System

Unread postby zain javed » Tue Apr 21, 2015 6:15 pm

Assignment # 2
"Introduction to Operating System"
Name: Zain Javed
Cms: 14075
Faculty: Feas
Subject: Programming Fundamentals
Section: A
Batch: 2014-2018

What is an operating system???
1: It hides the details of various hardware configuration.
2: For each possible device that might be present on a system the application do not need to be tailored.

1: It Manages excess to shared hardware resources.
2: To share the same hardware it enables multiple applications simultaneously.

Windows, Unix & Linux are some major operating systems of modern era and all of these operating systems has both advantages and disadvantages, There are four essential managers of every operating system and they all work as a unit to get their tasks done. The oerating system is the boss of all four managers & makes it sure that they all do there job equally and properly. The four managers are given below:-

1:Memory Manager:
The memory manager is a kind of utility that properly operates with our (OS) it checks every request from the memory and see that if it is valid or not valid, Memory manager allows the place of different memory spaces who are not already in use. Memory spaces may need to be de-allocated to free-up the space for other operations.

2:Process Manager:
The Process manager decides that how to allocate the brain of the computer i.e Central Processing Unit. It keeps the track record of every process that is happening in the operating system, it handles all the jobs that enters in a system and manages all the process which are linked up with those jobs.

3:Device Manager:
It monitors each and every device, channel and control unit, it need to choose the most efficient way to allocate all those devices which are attached/connected to the computer system i.e external hardrives, flashdrives, & printers etc

4:File Manager:
It checks each and every kind of file which is present in our computer, This means compiler, data files and all certain apps. It sets permission so that certain users see certain kind of files.

5:Network Manager:
Network manager is a very important part of essential managers, It provides a way for users to share both software and hardware resources at a time, while it also controls the user's access to them. It also makes the network more safer and easier for the user.
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