MCA211 – OPERATING SYSTEM BK ID B1405 NUMBER OF ASSIGNMNETS

ASSIGNMENT 

DRIVE SPRING- 2018

PROGRAM MASTER OF COMPUTER APPLICATION SEMESTER II

SUBJECT CODE & NAME MCA211 – OPERATING SYSTEM BK ID B1405 NUMBER OF ASSIGNMNETS, CREDITS & MARKS 2, 4 Credits,30 marks each  

ASSIGNMENT SET -1

Q.1. Differentiate between Sequential access and direct access methods.                                      10

Answer:-

Sequential access: - In this simple access method, information in a file is accessed sequentially one record after another. To process the i^th record all the i-1 records previous to i must be accessed. Sequential access is based on the tape model that is inherently a sequential access device. Sequential access is best suited where most of the records in a file are to be processed. For example, transaction files.

Direct access: - Sometimes it is not necessary to process every record in a file. It may not be necessary to process records in the order in which they are present. Information present in a record of a file is to be accessed only if some key value in that record is known. In all such cases, direct access is used. Direct access is based on the disk that is a direct access device and allows random access of any file block. Since a file is a collection of physical blocks, any block and hence the records in that block are accessed. For example, master files. Databases are often of this type since they allow query processing that involves immediate access to large amounts of information. All reservation systems fall into this category. Not all operating systems support direct access files. Usually files are to be defined as sequential or direct at the time of creation and accessed accordingly later. Sequential access of a direct access file is possible but direct access of a sequential file is not.

Q.2. Differentiate between Daisy chain bus arbitration and Priority encoded bus arbitration.       10

Answer:-

Daisy chain arbitration	Priority encoded arbitration
The requesting device or devices assert the signal bus request.	Each device has a request line connected to a centralized arbiter that determines which device will be granted access to the bus.
The bus arbiter returns the bus grant signal, which passes through each of the devices which can have access to the bus	The order may be fixed by the order of connection (priority encoded), or it may be determined by some algorithm preloaded into the arbiter.

Daisy chain arbitration:-

Figure.a Here, the priority of a device depends solely on its position in the daisy chain. If two or more devices request the bus at the same time, the highest priority device is granted the bus first, and then the bus grant signal is passed further down the chain. Generally a third signal (bus release) is used to indicate to the bus arbiter that the first device has finished its use of the bus. Holding bus request asserted indicates that another device wants to use the bus.

Fig.a: Daisy chain bus arbitration

Priority encoded arbitration:-

Figure b. shows this type of system. Note that each device has a separate line to the bus arbiter. (The bus_grant signals have been omitted for clarity.)

Fig.b: Priority encoded bus arbitration