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 batch operating system. Explain its advantages and disadvantages.

Answer: To avoid the problems of early systems the batch processing systems were introduced. The problem of early systems was more setup time. So the problem of more set up time was reduced by processing the jobs in batches, known as batch processing system. In this approach similar jobs were submitted to the CPU for processing and were run together.

The main function of a batch processing system is to automatically keep executing the jobs in a batch. This is the important task of a batch processing system i.e. performed by the 'Batch Monitor' resided in the low end of main memory.

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

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 being moved

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. If the requested address is present in the TLB, the CAM search yields a match quickly and

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:

11000011000000111001111110001111…

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.

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