CS604 Final Term Solved Subjective 2015 by Aabi Ali

Q1. 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.

Q2. 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

Q3. 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

Q4. 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.

Q5. what are possible ways to recover a system from deadlock.

Recovery from Deadlock

Q6. what are the problems that can occur while trying to violate the condition of hold and wait for deadlock .

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

Q7. 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). � Can have a single input queue instead of one for each partition. � So that if there are no big jobs can use big partition for little jobs. � Can think of the input queue(s) as the ready list(s) with a scheduling policy of FCFS in each partition. � The partition boundaries are not movable and are set at boot time (must reboot to move a job). � MFT can have large internal fragmentation, i.e., wasted space inside a region � Each process has a single ``segment'' (we will discuss segments later) � No sharing between processes. � No dynamic address translation. � At load time must ``establish addressability''. � Must set a base register to the location at which the process was loaded (the bottom of the partition). � The base register is part of the programmer visible register set. � This is an example of address translation during load time. � Also called relocation. � Storage keys are adequate for protection (IBM method). � Alternative protection method is base/limit registers. � An advantage of base/limit is that it is easier to move a job. � But MFT didn't move jobs so this disadvantage of storage keys is moot.