Operating system interview questions for freshers

          

Operating system interview questions for freshers


What is graceful degradation?
What are loosely coupled systems?
Explain SMP.
What is DLM?
Explain the handheld systems .List the issues related to the handheld system.
Why is interrupt vector used in operating systems?
What is the need of device status table?
How can the speed of interrupt driven input output systems be improved?
Explain the execution cycle for a von Neumann architecture.
Explain the positioning time for a disk.

What is graceful degradation?

• It is the ability to continue providing service proportional to level of hardware.
• Systems designed for graceful degradation are called fault tolerant.
• If we have several processors connected together, then failure of one would not stop the system.
• Then the entire system runs only 10% slower.
• This leads to increased reliability of the system.

What are loosely coupled systems?

• These systems are also called as the distributed systems.
• It consist of collection of processors that do not share memory or clock.
• The processors communicate through high speed buses or telephone lines.
• It can be a centralized system where the server responds to client requests.
• It can also be a peer to peer system.

Explain SMP.

• It is called as symmetric multiprocessing which is multiprocessor system.
• In it each processor runs an identical copy of the operating system.
• These copies communicate with one another as needed.
• These processor systems lead to increased throughput.
• These systems are also called parallel systems or tightly coupled systems.

What is DLM?

• It is the service called as distributed lock manager.
• In cluster systems to avoid file sharing the distributed systems must provide the access control and file locking.
• This ensures that no conflicting operations occur in the system.
• Here the distributed file systems are not general purpose therefore it requires locking.

Explain the handheld systems .List the issues related to the handheld system.

• Handheld devices are palm tops and cellular telephones with connectivity to a network.
• These devices are of limited size which leads to limited applications.
• They use a memory 512KB to 16MB as a result the operating system and applications must use the memory efficiently.
• The speed of the processors is only a fraction of speed of the PC processors and for faster processors larger battery is required.
• These devices use very small display screens so reading mails and browsing must be condensed to smaller displays.

Why is interrupt vector used in operating systems?

• The operating system these days are interrupt driven and this requires the interrupt vector.
• This interrupt vector contains the addresses of the interrupt service routines for various devices.
• Here the interrupts can be indirectly called through the table with no intermediate routine needed.
• This leads to interrupt handling at a faster rate.
• Operating systems like MS DOS and UNIX are using the interrupt vector.

What is the need of device status table?

• This table gives the device type, its address and status.
• It is required to keep a track of many input output requests at the same time.
• The state of the device can be functioning, idle or busy.
• If a device is busy ,type of request and other parameters are stored in the table entry.
• If more than one processor issues request for the same device then a wait queue is maintained.

How can the speed of interrupt driven input output systems be improved?

• Direct memory access is used to enhance the speed of the input output systems.
• Here buffers ,counters and pointers are set for the devices.
• The device controller transfers the block of data directly from own buffer storage to memory.
• The data is not given to the CPU for further transfer between CPU and input output device or CPU and memory.
• Only one interrupt is generated per block than one interrupt per byte which enhances the speed.

Explain the execution cycle for a von Neumann architecture.

• Initially the system will fetch the instruction and stores it in instruction register.
• Instruction is then decoded and may cause operands to be fetched from memory.
• After execution the result is stored in the memory.
• Here the memory unit sees only the memory addresses irrespective of how they are generated.
• Memory unit is also unaware of what addresses are for.

Explain the positioning time for a disk.

• It is also called as the random access time used by a disk to perform operations.
• It consists of time to move the disk arm to the desired cylinder called the seek time.
• The time required for the desired sector to rotate to the disk head is called rotational latency.
• Typical disks can transfer megabytes of data per second.
• Seek time and rotational latency is always in milliseconds.



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