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1. 

   AYESHA MUMTAZ on February 8, 2019 at 1:05 pm

   Q:1 Does pre-paging help to control the trashing ?justify with solid reason.
   An obvious property of a pure demand paging system is the large number of page faults
   that occur when a process is started. This situation is the result of trying to get the initial
   locality into memory. Pre-paging is an attempt to prevent this high level of initial paging.
   The strategy is to bring into memory at one time all the pages that will be needed.
   Q:2 List down two major benefits of Virtual Memory.
   • Virtual Memory is the separation of user logical memory from physical memory. This
   separation allows an extremely large virtual memory to be provided for programmers
   when only a smaller physical memory is available. • Virtual memory makes the task of
   programming easier because the programmer need not worry about the amount of
   physical memory
   Q:3 Write down the use of mounting and mount point in file system.
   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. There are types of mounts: Remote mount Local mount
   Q:4 In valid operating system name the system call that can be used to request
   memory map an opend file.
   In a UNIX system, mmap() system call can be used to request the operating system to
   memory map an opened file.
   Q:5 what are possible ways to recover a system from deadlock.
   Recovery from Deadlock
   When a deadlock detection algorithm determines that a deadlock exists, several
   alternatives exist. One possibility is to inform the operator that a deadlock has occurred,
   and to let the operator deal with the deadlock manually. The other possibility is to let the
   system recover from the deadlock automatically. There are two options for breaking a
   deadlock. One solution is simply to abort one or more processes to break the circular
   wait. The second option is to preempt some resources from one or more of the
   deadlocked processes.
   Q:6 what are the problems that can occur while trying to violate the condition of
   hold and wait for deadlock .
   To ensure that the hold and wait condition does not occur in a system, we must
   guarantee that whenever a process requests a resource, it does not hold any other
   resources. One protocol that can be used requires each process to request and be
   allocated all its resources before it begins execution
   Q:7 Difference between MVT and MFT?
   Multiprogramming with Variable Tasks (MVT)
   This is the generalization of the fixed partition scheme. It is used primarily in a batch
   environment. This scheme of memory management was first introduced in IBM OS/MVT
   (multiprogramming with a varying number of tasks). Here are the main characteristics of
   MVT.
   � Both the number and size of the partitions change with time.
   � Job still has only one segment (as with MFT) but now can be of any size up to the
   size of the machine and can change with time.
   � A single ready list.
   � Job can move (might be swapped back in a different place).
   � This is dynamic address translation (during run time).
   � Must perform an addition on every memory reference (i.e. on every address
   translation) to add the start address of the partition.
   Q8 Multiprogramming with Fixed Tasks (MFT)
   In this technique, memory is divided into several fixed-size partitions. Each partition may
   contain exactly one process. Thus the degree of multiprogramming is bound by the
   number of partitions. In this multiple partition method, when a partition is free, a process
   is selected from the input queue and is loaded in the free partition. When the process
   terminates, the partition becomes available for another process
   � This was used by IBM for system 360 OS/MFT (multiprogramming with a fixed
   number of tasks).