Overview Of Operating System

Overview Of Operating System

Q.1 what is an Operating System? What are the basic functions of an

Operating System?

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.

The basic functions of an operating system are:

Ø Booting the computer

Ø A part of the computing sys. That manages all h/w, s/w.

Ø It controls files,devices,every memory section, and every nanosecond of processing time.

Ø When user sends a command, the operating system makes sure that the commandis executed.

Ø If its not executed,os must arrange for the user to get a message explainingthe error.

Ø Provides a user interface, e.g. graphical user interface (GUI)

Ø In short – it’s the boss.

 

Q.2 Explain OS as a memory manager. Or write a short note on managers of the operating system. (2013)

Four essential managers of every operating system are as follows

1)  memory manager

2)  processor manager

3)  device manager

4)  file manager

Each manager works closely with the other manager and performs its unique role.Memory manager is in charge of main memory also known as RAM. It checks the validity of each request for memory space and if it is a legal request, the memory manager allocates a portion that is not already in use. In a multi-user environment, the memory manager sets up a table to keep track of who is using which section of memory. Finally, when the time comes to reclaim the memory, the memory manager deallocates the memory.A primary responsibility of the memory manager is to preserve the space in main memory occupied by the operating system itself. It can not allow any part of it to be accidentally or intentionally.

 

Q.3 How does OS behave as a process manager.

Processmanager decides how to allocate the CPU. An important function of the Processmanager is to keep the track of status of each process.

-       It monitors whether the cpu is executing a process or waiting.

-       Process manager has 2 levels of responsibility.

1)  To handle the job as they enter the system. Handled by Job Scheduler.

§  it’s a high level portion of process manager.

§  Has power to accepts/rejects incoming calls.

2)  To manage each process within this job. Handled by Process Scheduler.

§  it’s a low level portion of process manager.

§  decides which process gets cpu, for how long time.

 

Q.4 Explain the role of an OS as a device manager.

It monitors every device, channel and control unit.  It makes allocations, start it operations and finally de-allocation of device.

 

Q.5 How does OS perform the function as a file manager?

It keeps the track of every file in the system including data files, assemblers, compilers, and application programs.

It enforces restriction on who has access to which files. It also controls what users are allowed to do with files once they access them.

 

Q.6 State the role of an OS as a network manager.

Operating systems with networking capability have a fifth essential manager called the Network manager.

It provides a convenient way for user to share resources include hardware (cpu, memory area, printer, tape driver, modem, disk drives) and software (compiler, application prog., data files)

 

Q.7 Explain the Types of OS. (2012) (2013)                     

Operating System is categorized in 5 types By response time.

1.   Batch system. :-  Batch system date from the earliest machines ,which relied on punched cards or a tape for input when job was entered by assembling the cards into a deck and running the entire deck of cards through a card reader as a group-a batch. Present days jobs are still processed serially without user interaction.

System Efficiency was measured in throughput( no. of jobs completed in parti. Given time). Turn around was measured in hours/days.

2.   Interactive sys.:- also called time sharing sys. Give a fasterturnaound than batch systembut slower then the real time systems. They were introduced to satisfy the demands of users who need fast turnaround when debugging their programs. User directly interacts with comp. sys. Via commands.  Response time measured in minutes/seconds.

3.   Real time sys.:-it is the fastest and are used in time- critical environments where data must be processed extremely quickly because the output influences immediate decision. Real time system are used for space flights, high speed aircraft, industrial process, sophisticated medical equipments etc… A real time system must be 100% responsive 100% of the time.   Response time measured in fraction of seconds.

4.  Hybrid sys. :-It is a combination of batch & interactive.They  Appear to be interactive because individual user can access the system via terminals and get response, but such system actually accepts and runs batch programs in the background when the interactive load s light.

5.   Embedded sys.:-Embedded sys are computer placed inside other products to add features,capabilities. It is used in automobiles, digital music players, elevators, pacemakers. Each set is designed to perform specific group of tasks.