Operating system paper june 2015

UNIT 1

Q1:- What is Bare Machine ?
Ans:-

Bare Machine is a computer used to be worked directly in machine language, without any system software support.
Bare Machine is a computer without any Operating system.
Computer used to be programmed directly is like user-unfriendly.
It is very trediopus to code a computer directly in machine language.
In market newly purchased computer without any operating system is like a bare machine on which operating system have to be installed to make it user friendly.
It creates backup point in the computer when the operating system is corrupted or at the time of destroy your computer.


Q2:- What is the purpose of System Calls?
Ans:-


 A system call is a program that describes how a program requests a service from kernel of operating system. 
This may include services like accessing hard disk.
These calls provide an interface between operating system and a process.
Purpose of system calls are given as follows:
·Basic purpose: Calls provide basic functionality to users to operate the operating system.
·Process control: System calls loads, execute and create processes and terminate when the user’s task is finished.
·File management: It provides file management such as creating a file, deleting it, open, close and save it. It also provides read, write functionalities.
·Device management: All hard disks are managed by system calls such as requesting adding , releasing, reading and writing the device.
·Information maintenance: System calls helps in making information maintenance such as get/set time or date, get/set data of system etc.
·Communication between processes: System calls are useful for creating and deleting communications, sending or receiving messages. They help in attaching or detaching remote devices and in transfer of status information

Q3:- How a Time Sharing Operating System differ from Batch Operating System
Ans:-


Batch operating systems:
A batch is a sequence of jobs. This batch is submitted to batch processing operating systems, and output would appear some later time in the form of a program or as program error. To speed up processing similar jobs are batched together.
The major task of batch operating systems is to transfer control automatically from one job to next. Here the operating is always in the memory.
1.    It is lack of interaction between user and job while executing
2.    Turnaround time is more.
3.    CPU is often idle, because of 1/0 devices are very slow.
Time sharing:
Time sharing or multi tasking is a logical execution of multiprogramming. Multiple jobs are executed by the CPU switching between them. Here the computer system provides on line communication between the user and the
system.
Here the CPU is never idle. Time shared operating system allows many users to share
the computer simultaneously.
Time sharing systems requires some sort of memory management and protection.

Q4:- How many types of Operating Systems are there explain each of them ?
Ans:-


Batch operating system
The users of a batch operating system do not interact with the computer directly. Each user prepares his job on an off-line device like punch cards and submits it to the computer operator. To speed up processing, jobs with similar needs are batched together and run as a group. 
The suitability of this type of processing is in programs with large computation time with no need of user interaction/involvement. Some examples of such programs include payroll, forecasting, statistical analysis and large scientific number crunching programs., Users are not required to wait while the job is being processed. They can submit their programs to operators and return later to collect them.
The problems with Batch Systems are as follows −
·                     Lack of interaction between the user and the job.
·                     CPU is often idle, because the speed of the mechanical I/O devices is slower than the CPU.
·                     Difficult to provide the desired priority.

Time-sharing operating systems
Time-sharing is a technique which enables many people, located at various terminals, to use a particular computer system at the same time.
Processor's time which is shared among multiple users/processes simultaneously is termed as time-sharing.
Multiple jobs are executed by the CPU by switching between them, but the switches occur so frequently. Thus, the user can receive an immediate response. 
For example, in multiples task executing simultaneously, time is shared between each task.
The operating system uses CPU scheduling and multiprogramming to provide each user with a small portion of a time. 
Advantages of Timesharing operating systems are as follows −
·                     Provides the advantage of quick response.
·                     Avoids duplication of software.
·                     Reduces CPU idle time.
Disadvantages of Time-sharing operating systems are as follows −
·                     Problem of reliability.
·                     Question of security and integrity of user programs and data.
·                     Problem of data communication.

Distributed operating System
The processors communicate with one another through various communication lines (such as high-speed buses or telephone lines). These are referred as loosely coupled systems or distributed systems.
Processors in a distributed system may vary in size and function. These processors are referred as sites, nodes, computers, and so on.
The advantages of distributed systems are as follows −
·                     With resource sharing facility, a user at one site may be able to use the resources available at another.
·                     Speedup the exchange of data with one another via electronic mail.
·                     If one site fails in a distributed system, the remaining sites can potentially continue operating.
·                     Better service to the customers.
·                     Reduction of the load on the host computer.
·                     Reduction of delays in data processing.

Network operating System
A Network Operating System runs on a server and provides the server the capability to manage many networking functions like data, user. 
The primary purpose of the network operating system is to allow shared file and printer access among multiple computers in a network, over a LAN, WAN etc.
Examples of network operating systems include Microsoft Windows Server 2003, Microsoft Windows Server 2008, UNIX, Linux, Mac OS X, Novell NetWare, and BSD.
The advantages of network operating systems are as follows −
·                     Centralized servers are highly stable.
·                     Security is server managed.
·                     Upgrades to new technologies and hardware can be easily integrated into the system.
·                     Remote access to servers is possible from different locations and types of systems.
The disadvantages of network operating systems are as follows −
·                     High cost of buying and running a server.
·                     Dependency on a central location for most operations.
·                     Regular maintenance and updates are required.
Real Time operating System
Real Time operating system which are used in environments where a large number of events mostly external to computer systems, must be accepted and processed in a certain deadlines. 
Examples of such applications are flight control, real time simulations etc. Real time systems are also frequently used in military application.
A real-time operating system must have well-defined, fixed time constraints, otherwise the system will fail. 
For example, Scientific experiments, medical imaging systems, industrial control systems, weapon systems, robots, air traffic control systems, etc.
There are two types of real-time operating systems.
Hard real-time systems
Hard real-time systems guarantee that critical tasks complete on time. In hard real-time systems, secondary storage is limited or missing and the data is stored in ROM. In these systems, virtual memory is almost never found.
Soft real-time systems
Soft real-time systems are less restrictive. A critical real-time task gets priority over other tasks and retains the priority until it completes. Soft real-time systems have limited utility than hard real-time systems. For example, multimedia, virtual reality, Advanced Scientific Projects like undersea exploration and planetary rovers, etc.


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