BT0070, Operating Systems

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Assignment

DRIVE	SPRING 2015
PROGRAM	BSc IT
SEMESTER	2
SUBJECT CODE & NAME	BT0070, Operating Systems
BK ID	B0954
CREDIT & MARKS	4 CREDITS & 60 MARKS

Note: Answer all questions. Each question is followed by evaluation scheme.

1. Write short notes on:

1. Process Creation

• Answer: There are four principal events that cause processes to be created:
1. System initialization. When an OS is booted, typically several processes are created.
2. Execution of a process creation system call by a running process. Often a running process will issue system calls to create one or more new processes to help it do its job. Creating new processes is particularly useful when the work to be done can easily be formulated in terms of several related, but otherwise independent interacting processes.
3. A user request to create a new

2. Terminating Process

Answer: A process terminates when it finishes executing its last statement. Its resources are returned to the system, it is purged from any system lists or tables, and its process control block (PCB) is erased i.e., the PCB's memory space is returned to a free memory pool. The new process terminates the existing process, usually due to following reasons:

Q. 2 Write short notes on:

1. Critical section problem

Answer: Critical section problem is defined as :

·         Set of instructions that must be controlled so as to allow exclusive access to one process

·         Rarely: access to the critical section is limited to n processes instead of one process

·         Execution of the critical section by processes is mutually exclusive in time

Q.3   What are TLBs? Why they are required in paging?

Answer: A translation look aside buffer (TLB) is a cache that memory management hardware uses to improve virtual address translation speed. The majority of desktop, laptop, and server processors includes one or more TLBs in the memory management hardware, and it is nearly always present in any hardware that utilizes paged or segmented virtual memory.

The TLB is sometimes implemented as content-addressable memory (CAM). The CAM search key is the virtual address and the search result is a physical address

Q.4  Describe the techniques of free space management of free space list.

Answer: Techniques of free space management:

Bit-Vector

Frequently, the free-space list is implemented as a bit map or bit vector. Each block is represented by a 1 bit. If the block is free, the bit is 0; if the block is allocated, the bit is 1.

For example, consider a disk where blocks 2, 3, 4, 5, 8, 9, 10, 11, 12, 13, 17, 18, 25, 26, and 27 are free, and the rest of the blocks are allocated. The free-space bit map would be:

Q.5 What are computer viruses? How do they affect our system?

Answer: A Computer virus is a small program that interferes with normal functions of the computer. Usually a virus program is attached to a computer file. The file to which a virus is attached is called infected file. When the infected file is copied on a disk, the virus is also copied and It hides itself on the disk.

Activation of a Virus

6. List and explain the types of multiprocessor OS.

Answer: Multiprocessing refers to an operating situation where the simultaneous processing of programs takes place. This state of ongoing and coordinated processing is usually achieved by interconnecting two or more computer processors that make it possible to use the available resources to best advantage. Many operating systems today are equipped with a multiprocessing capability, although multiprogramming tends to be the more common approach today.

The basic platform for multiprocessing allows for

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