CS604- OPERATING SYSTEM FINAL TERM PAPER

SOLVED SUBJECTIVE

SPRING 2011

TOTAL MARKS : 40
TIME ALLOWED :120MIN

QNo.1   What is mounting? Name two types of mounting. Give your answer with respect to File System?   (MARKS  :  2)

Answer:-

Mounting makes file systems, files, directories, devices, and special files available for use at a particular location. Mount point is the actual location from which the file system is mounted and accessed. You can mount a file or directory if you have access to the file or directory being mounted and write permission for the mount point

There are types of mounts:

1. Remote mount
2. Local mount      

QNo.2   How to implement hold and wait which can ensure that a deadlock will not occur?   (MARKS  :  2)

Answer:-

A process must be holding at least one resource and waiting to acquire additional resources that are currently being held by other processes.

QNo.3   what is the purpose of “stub” in dynamic linking, give answer with respect to memory?   (MARKS  :  2)

Answer:-

With dynamic linking, a stub is included in the image for each library-routine reference. This stub is a small piece of code that indicates how to locate the appropriate memory-resident library routine or how to load the library if the routine is not already present. During execution of a process, stub is replaced by the address of the relevant library code and the code is executed .If library code is not in memory, it is loaded at this time

QNo.4 how page fault frequency can b used as a method of thrashing.   (MARKS  :  3)

Answer:-

Page fault frequency is another method to control thrashing. Since thrashing has a high page fault rate, we want to control the page fault frequency. When it is too high we know that the process needs more frames. Similarly if the page-fault rate is too low, then the process may have too many frames. The operating system keeps track of the upper and lower bounds on the page-fault rates of processes. If the page-fault rate falls below the lower limit, the process loses frames. If page-fault rate goes above the upper limit, process gains frames. Thus we directly measure and control the page fault rate to prevent thrashing.

QNo.5 File control block? (MARKS  :  3)

Answer:-

A file control block is a memory data structure that contains most of the attributes of a file. In UNIX, this data structure is called inode (for index node).

QNo.6 Define Roll in & Roll out with respect to swapping? (MARKS  :  3)

Answer:-

A process needs to be in the memory to be executed. A process, however, can be swapped temporarily out of memory to a backing store, and then brought back into memory for continued execution. Backing store is a fast disk large enough to accommodate copies of all memory images for all users; it must provide direct access to these memory images. The system maintains a ready queue of all processes whose memory images are on the backing store or in memory and are ready to run. This technique is called roll out, roll in.

QNo.7 Write one advantage and one disadvantage of using large size block? (MARKS  :  5)

Answer:-

Advantages:-

If you use larger block then relatively less overhead. Per I/O you can fetch more data. This is very good for sequential access, or very large rows. 

Disadvantages:-

Large block size is not good for index blocks used in an OLTP(Online Transaction Processing) type environment, because they increase block contention on the index leaf blocks.

QNo.8 Explain the FIFO page algorithm with a scenario where the Belady’s anomaly true? (MARKS  :  5)

Answer:-

The problem with this algorithm is that it suffers from Belady’s anomaly: For some page replacement algorithms the page fault rate may increase as the number of allocated 199

frames increases, whereas we would expect that giving more memory to a process would improve its performance.

QNo.9 writes the formula to calculate page table size     ? (MARKS  :  5)

Answer:-

Page table size = NP * PTES , where NP is the number of pages in the process address space and PTES is the page table entry size (equal to |f| based on our discussion so far).

QNo.10Difference between deadlock avoidance and deadlock (snowz) prevention?  (MARKS  :  5)

 Answer:-

1. Deadlock prevention: is a set of methods for ensuring that at least one of the necessary conditions cannot hold. These methods prevent deadlocks by constraining how processes can request for resources.

2. Deadlock Avoidance: This method of handling deadlocks requires that processes give advance additional information concerning which resources they will request and use during their lifetimes. With this information, it may be decided whether a process should wait or not.

                                                                    GOOD LUCK