Operating System (OS) Interview Questions And Answers - Part V.

21. List Five Services Provided By An Operating System. Explain How Each Provides Convenience To The Users. Explain Also In Which Cases It Would Be Impossible For User-Level Programs To Provide These Services.

• PROGRAM EXECUTION: The operating system loads the contents (or sections) of a file into memory and begins its execution. A user-level program could not be trusted to properly allocate CPU time.

• I/O OPERATIONS: Disks, tapes, serial lines, and other devices must be communicated with at a very low level. The user need only specify the device and the operation to perform on it, while the system converts that request into device or controller specific commands. User-level programs cannot be trusted to only access devices they should have access to, and to only access them when they are otherwise unused.

• FILE-SYSTEM MANIPULATION: There are many details in file creation, deletion, allocation, and naming that users should not have to perform. Blocks of disk space are used by files and must be tracked. Deleting a file requires removing the name file information and freeing the allocated blocks. Protections must also be checked to assure proper file access. User programs could ensure neither adherence to protection methods nor could they be trusted to allocate only free blocks and de-allocate blocks on file deletion.

• COMMUNICATIONS: Message passing between systems requires messages be turned into packets of information, sent to the network controller, transmitted across a communication medium, and reassembled by the destination system. Packet ordering and data correction must take place. Again, user programs might not coordinate access to the network device, or they may receive packets destined for other processes.

• ERROR DETECTION: Error detection occurs at both the hardware and software levels. At the hardware level, all data transfers must be inspected to ensure that data have not been corrupted in transit. All data on media must be checked to be sure they have not changed since they were written to the media. At the software level, media must be checked for data consistency; for instance, do the numbers of allocated and unallocated blocks of storage match the total number on the device. There, errors are frequently process-independent (for instance, the corruption of data on a disk), so there must be a global program (the operating system) that handles all types of errors. Also, by having errors processed by the operating system, processes need not contain code to catch and correct all the errors possible on a system.

22. Define The Essential Properties Of Batch Operating System?

Essential properties of Batch Operating System:

• Jobs with similar needs are batched together and run through the computer as a group, by an operator or automatic job sequencer.
• Performance is increased by attempting to keep CPU and I/O devices busy at all times through buffering, off-line operation, spooling, and multiprogramming.

23. Define The Essential Properties Of Interactive Operating System?

Essential properties of Interactive Operating System:

• Composed of many short transactions with input and output read/written on the screen; the results and timing of the next transaction may be unpredictable.
• Note that a purely interactive system (no time-sharing) only has one user; e.g., a PC).

24. Define The Essential Properties Of Time Sharing Operating System?

Essential properties of Time-sharing Operating System:

• Uses CPU scheduling and multiprogramming to provide economical interactive use of a system.
• The CPU switches rapidly from one user to another.

25. Define The Essential Properties Of Real Time Operating System?

Essential properties of Real-time Operating System:

• The system must respond to inputs/commands within a fixed amount of time to ensure correct performance.
• Input is typically read from sensors.

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26. Define the essential properties of Distributed operating system?
27. What do you mean by distributed system? Why are distributed systems desirable?
28. What are the advantages of Distributed Operating System?
29. What is a process? What are the different process states?
30. Please show the state diagram & state transition of the process?

31. What are the advantages of using a higher level language to implement an operating system?
32. Distinguish between system and application programs.
33. State 3 methods used to pass parameters to the Operating System?
34. State a few reasons why a process may terminate the execution of one of its children?
35. What resources are used when a thread is created? How do they differ from those used when a process is created?

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