File access method

                              File access method stores information when it is used this information must be access and read into a computer memory this information in the file can be access by several ways:


1)         sequential method:

                                               Simplest method of access in sequential method information in the file is resided in the order, one record after another. This method of access it the most comman.


                                         The bulks of operations on a file is read and write, read operations read next poison of the file and automatically move the pointer to the next block. Similarly bright upend to the end of the file such a file can be reset to the beginning and on sum system a program may be able to skip forward or backward record.


2)         Direct access method:

                                                Another method is direct access; a file is med up fix length, logical record that allows program to read write record repitaly in no particular order the direct modal of file since disk allow random access (direct access) to any file block for direct access the file is view as number of sequences of blocks or record the direct access file allows arbitrary block to be read or write so we any read block 14 the read 53 and then write block 7.


                           Direct access file are of great use of immediate access to large amount of information data basis are off on of this type when a query consulting a particular subject arise being computer which block contains the answer and then read that block directly to provide the desired information .


                           For the direct access method the operation most be modify to include the block number as a parameter so we have read n , where n is a block number rather then read next and alternative approach is to retain read next and write next as with sequences access and to add operation position file to n ,where n is the block number.                       

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by dhruvi   chaudhari  in Operating System  on 3/3/2015 1:56:49 AM  

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