BT0070, Operating Systems

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Assignment

DRIVE	FALL 2014
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 Describe the mechanism of process creation in an OS.

Answer: Process creation is only the first management action performed by the OS on the process. Since the process will use the resources made available by the OS, further OS activity will typically be needed to manage those resources on behalf of the process. This involves the release of the CPU control from the process to the OS. This release is triggered by various conditions that can usually be classified as follows:

2 Suppose that the following processes arrive for execution at the times indicated.

Process                Burst Time

P1                           24

P2                           3

P3                           3

1. Suppose the process arrives in the order P1, P2, P3 and

2. Suppose the process arrive in the order P2, P3, P1.

For both the above situation draw the Grantt Chart and calculate the waiting time for each process and average waiting time.

Answer: Suppose that the processes arrive in the order: P1 , P2 , P3 ,The Gantt Chart for the schedule is:

Waiting time for P1 = 0; P2 = 24; P3 = 27, Average waiting time: (0 + 24 + 27)/3 = 17 Suppose that the

processes arrive in the order P2 , P3

3 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

2. Buffering

Answer: It is a process of storing data in memory area called Buffers while data is being transferred between two devices or between a device and an application. Buffering is done for 3 reasons: a. To cope with the speed mismatch between producer (or sender) and consumer (or receiver) of a data stream. b. To adapt between the devices having different data-transfer size. c. To support copy semantics for application I/O. a data buffer (or just buffer) is a region of a physical memory storage used to temporarily store data while it is

4 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.

5 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:

11000011000000111001111110001111…

6 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

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