CS604 Final Term Solved Subjective with References by Moaaz

CS604- Operating Systems · Solved Subjective · From Final term Papers · 10 July,2013 · PSMD01 · 1. Write the names of common file structures. (2)

Answer: (Page 214)

•  None
•  Simple record structure
•  Complex Structures

2. Which part of compiler/assembler perform the task of taking one or more objects generated

and assemble them in to a single executable program. (2)

Linking means taking one or more objects generated by compilers and assemble them into a single executable program.

3.Write the method through which Linus/Unix commands can communicate with each other. (2)

4. Consider a process having its segment 15 having 5096 bytes. The process generates a logical address (15, 3921). What page does the logical address refers to? (2)

Answer: (Page 181) ceiling[3921/1024]= 4 (i.e., page number 3)

5. What is mounting? Name its two types. (3)

Answer: (Page 225) 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

7. Which term is best suited for the situation where several process access and manipulate shared data concurrently and final value of data depend which process finishes last. (3)

Answer: (Page 96) A situation like this, where several processes access and manipulate the same data concurrently and the outcome of the manipulation depends on the particular order in which the access takes place, is called a race condition.

8. What is difference between deadlock avoidance and deadlock prevention. (3)

Answer: (Page 132)

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.
3. A file system must keep track of free blocks on disk. Name two schemes for doing this, and one advantage for each (5)

Linked list of free pages supports very fast deletion: we can link a whole file onto the free list in constant time. Bit map facilitates spatial locality optimizations in disk layout. It is also the most effecient in terms of memory inside the OS required to find the free pages. The list of pages with free page references in each is also space-efficient, particularly for disks that are mostly full (the bit map takes space proportional to the size of the entire disk). Also, free page insertion and deletion operations exhibit high locality under this scheme.

10. Differentiate between logical and physical address. (5)

Answer: (Page 152) An address generated by the CPU is commonly referred to as a logical address, where as an address seen by the memory unit–that is, the one loaded into the memory-address register of the memory–is commonly referred to as the physical address. In essence, logical data refers to an instruction or data in the process address space where as the physical address refers to a main memory location where instruction or data resides.

The compile time and load time binding methods generate identical logical and physical addresses, where as the execution time binding method results in different physical and logical addresses. In this case we refer to the logical address as the virtual address. The set of all logical addresses generated by a program form the logical address space of a process; the set of all physical addresses corresponding to these logical addresses is a physical address space of the process. The total size of physical address space in a system is equal to the size of its main memory.

The run-time mapping from virtual to physical addresses is done by a piece of hardware in the CPU, called the memory management unit (MMU).

11. Identify the necessary information that must be stored in process control block during the execution of program. (5)

12. What steps are needed for page replacement? (5)

Answer: (Page 196)

1. Find the location of the desired page on the disk

Q2. Find a free frame

1. If there is a free frame use it.
2. If there is no free frame, use a page replacement algorithm to select a victim frame.
3. Read the desired page into the newly freed frame; change the page and frame tables.
4. Restart the user process.

QNo.1 Name of three major frame allocation schemes?

Answer: (Page 204) There are three major allocation schemes:

•  Fixed allocation
•  Proportional Allocation
•  Priority allocation

QNo.2 how to protection of files and giving access to be secured in UNIX ?

Answer: (Page 229) UNIX recognizes three modes of access: read, write, and execute (r, w, x). The execute permission on a directory specifies permission to search the directory.

QNo.3 what is lazy analyzer that is use in virtual memory?

Answer: (Page 186) When we want to execute a process, we swap it into memory. Rather than swapping the entire process into memory, however we use a lazy swapper.

QNo.4 Differentiate between Cache and CPU Register ?

CPU register is just a small amount of data storage that facilitates some CPU operations. CPU cache, it is a high speed volatile memory which is bigger in size, that helps the processor to reduce the memory operations.