Tuesday, October 6

Operating System-IV


1. Describe the Buddy system of memory allocation.
Free memory is maintained in linked lists, each of equal sized blocks. Any such block is of size 2^k. When some memory is required by a process, the block size of next higher order is chosen, and broken into two. Note that the two such pieces differ in address only in their kth bit. Such pieces are called buddies. When any used block is freed, the OS checks to see if its buddy is also free. If so, it is rejoined, and put into the original free-block linked-list.
2. What is time-stamping? - It is a technique proposed by Lamport, used to order events in a distributed system without the use of clocks. This scheme is intended to order events consisting of the transmission of messages. Each system 'i' in the network maintains a counter Ci. Every time a system transmits a message, it increments its counter by 1 and attaches the time-stamp Ti to the message. When a message is received, the receiving system 'j' sets its counter Cj to 1 more than the maximum of its current value and the incoming time-stamp Ti. At each site, the ordering of messages is determined by the following rules: For messages x from site i and y from site j, x precedes y if one of the following conditions holds....(a) if Ti

3. How are the wait/signal operations for monitor different from those for semaphores? - If a process in a monitor signal and no task is waiting on the condition variable, the signal is lost. So this allows easier program design. Whereas in semaphores, every operation affects the value of the semaphore, so the wait and signal operations should be perfectly balanced in the program.
4. In the context of memory management, what are placement and replacement algorithms? - Placement algorithms determine where in available real-memory to load a program. Common methods are first-fit, next-fit, best-fit. Replacement algorithms are used when memory is full, and one process (or part of a process) needs to be swapped out to accommodate a new program. The replacement algorithm determines which are the partitions to be swapped out.

5. In loading programs into memory, what is the difference between load-time dynamic linking and run-time dynamic linking? - For load-time dynamic linking: Load module to be loaded is read into memory. Any reference to a target external module causes that module to be loaded and the references are updated to a relative address from the start base address of the application module.
With run-time dynamic loading: Some of the linking is postponed until actual reference during execution. Then the correct module is loaded and linked.

6. What are demand- and pre-paging? - With demand paging, a page is brought into memory only when a location on that page is actually referenced during execution. With pre-paging, pages other than the one demanded by a page fault are brought in. The selection of such pages is done based on common access patterns, especially for secondary memory devices.

7. Paging a memory management function, while multiprogramming a processor management function, are the two interdependent? - Yes.
8. What is page cannibalizing? - Page swapping or page replacements are called page cannibalizing.
9. What has triggered the need for multitasking in PCs? - Increased speed and memory capacity of microprocessors together with the support fir virtual memory and
Growth of client server computing
10. What are the four layers that Windows NT have in order to achieve independence?
Hardware abstraction layer
Kernel
Subsystems
System Services.
11. What is SMP? - To achieve maximum efficiency and reliability a mode of operation known as symmetric multiprocessing is used. In essence, with SMP any process or threads can be assigned to any processor.
12. What are the key object oriented concepts used by Windows NT?
Encapsulation
Object class and instance
13. Is Windows NT a full blown object oriented operating system? Give reasons. - No Windows NT is not so, because its not implemented in object oriented language and the data structures reside within one executive component and are not represented as objects and it does not support object oriented capabilities .
14. What is a drawback of MVT?
It does not have the features like
ability to support multiple processors
virtual storage
source level debugging
15. What is process spawning? - When the OS at the explicit request of another process creates a process, this action is called process spawning.
16. How many jobs can be run concurrently on MVT?
15 jobs
17. List out some reasons for process termination.
Normal completion
Time limit exceeded
Memory unavailable
Bounds violation
Protection error
Arithmetic error
Time overrun
I/O failure
Invalid instruction
Privileged instruction
Data misuse
Operator or OS intervention
Parent termination.
18. What are the reasons for process suspension?
swapping
interactive user request
timing
parent process request
19. What is process migration?
It is the transfer of sufficient amount of the state of process from one machine to the target machine
20. What is mutant? - In Windows NT a mutant provides kernel mode or user mode mutual exclusion with the notion of ownership.
21. What is an idle thread? - The special thread a dispatcher will execute when no ready thread is found.
22. What is FtDisk?
It is a fault tolerance disk driver for Windows NT.
23. What are the possible threads a thread can have?
Ready
Standby
Running
Waiting
Transition
Terminated.
24. What are rings in Windows NT? - Windows NT uses protection mechanism called rings provides by the process to implement separation between the user mode and kernel mode.
25. What is Executive in Windows NT?
In Windows NT, executive refers to the operating system code that runs in kernel mode.
26. What are the sub-components of I/O manager in Windows NT?
Network redirector/ Server
Cache manager.
File systems
Network driver
Device driver
27. What are DDks? Name an operating system that includes this feature.
DDks are device driver kits, which are equivalent to SDKs for writing device drivers. Windows NT includes DDks.
28. What level of security does Windows NT meets?
C2 level security.
29. What do you mean by deadlock? - A process enters a wait state and a waiting process will never change state because the resource that they have requested are held by another waiting process is called DEADLOCK.
30. Why paging is used ? - External Fragmentation : memory exists satisfy a request but is not contiguous, so storage is fragmented into large number of small holes.
PAGING : In the external fragmentation problem, the process is to be allocated physical memory and is done by paging. paging avoids the considerable problem of fitting the varying sized memory chunks(packets) on to the backing store.
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