ECO401 Final Term Objective

CS604- OPERATING SYSTEM · SOLVED SUBJECTIVE FOR FINAL EXAM · FALL SEMESTER 2012

QNo.1 Scan Algorithm is sometimes called the elevator algorithm, why?

Answer: The Scan algorithm is sometimes called the elevator algorithm, since the disk arm behaves like an elevator in a building servicing all the requests (people at floors), going up and then reversing to service the requests going down.

QNo.2 What is basic logic in FIFO page replacement algorithm?

must be replaced, the oldest page is chosen.

QNo.3 What is mounting? Name two types of mounting. Give your answer with respect to File System?

There are types of mounts:

1. Remote mount
2. Local mount

QNo.4 Write three main characteristics memory management System?

1. The purpose of memory management is to ensure fair, secure, orderly, and efficient use of memory.
2. The task of memory management includes keeping track of used and free memory space, as well as when, where, and how much memory to allocate and deallocate.
3. It is also responsible for swapping processes in and out of main memory

QNo.5 Summarize the tradeoffs among simple arrays, trees, and hash tables as implementations of a page table.

Arrays

Arrays, lists and tables are often allocated more memory than they actually need. An array may be declared 100 by 100 elements even though it is seldom larger than 10 by 10 elements.

Hash Tables

This is a common approach to handle address spaces larger then 32 bits .Usually open hashing is used. Each entry in the linked list has three fields: page number, frame number for the page, and pointer to the next element

QNo.6 How to implement hold and wait which can ensure that a deadlock will not occur?

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.7 List down 2 major benefits of virtual memory

1. 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.
2. Virtual memory makes the task of programming easier because the programmer need not worry about the amount of physical memory,

QNo.7 what are the possible system for the input redirection in the UNIX/LINX system

Answer: Linux redirection features can be used to detach the default files from stdin, stdout, and stderr and attach other files with them for a single execution of a command. The act of detaching defaults files from stdin, stdout, and stderr and attaching other files with them is known as input, output, and error redirection.

Here is the syntax for input redirection:

command < input-file or command 0< input-file

QNo.8 what is the purpose of “stub” in dynamic linking, give answer with respect to memory

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.9 Dynamic linking

Answer: Dynamic linking requires potentially less time to load a program. Less disk space is needed to store binaries. However it is a time-consuming run-time activity, resulting in slower program execution.

QNo.10 what is use of mounting in file system

accessed.

QNo.10 How operating attacks the" no preemption "condition necessary for feedback in order to solve the pro of deadlock

Answer: No preemption: Resources cannot be preempted. That is, after using it a process releases a resource only voluntarily.

QNo.11 What is pager? Give answer with respect to virtual memory

Answer: A pager is concerned with the individual pages of a process. Thus the term pager is used in connection with demand paging. When a process is to be swapped in, the paging software guesses which pages would be used before the process is swapped out again. Instead of swapping in a whole process, the pager brings only those necessary pages into memory.

QNo.12 what does the following command do in the LINX/UNIX operating system

Answer: $mkdir ~/courses/cs604/program Command creates the programs directory under your ~/courses/cs604 directory.

QNo.13 How you can differentiate between external and internal fragmentation

Answer: Fragmentation occurs in a dynamic memory allocation system when many of the free blocks are too small to satisfy any request.

External Fragmentation: External Fragmentation happens when a dynamic memory allocation algorithm allocates some memory and a small piece is left over that cannot be effectively used. If too much external fragmentation occurs, the amount of usable memory is drastically reduced. Total memory space exists to satisfy a request, but it is not contiguous.