24-01-2012, 11:28 AM
PRINCIPLES OF OPERATING SYSTEM
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Introduction....
access mechanism
When a file is used then the stored information in the file must be accessed and read into the memory of a computer system.various mechanism are provided to access a file from the operating system.
Some system provide only one access method while some support many access methods for files.
From many access methods to choose the right method for particular application,is a major design problem.
Some common files access mechanism are :
#sequential access
#direct access
#index access
Use of access methods...
.Ease of programming - programmer would no longer deal with a specific device procedures, including error detection and recovery tactics in each and every program. A program designed to process a sequence of 80-character records would work no matter where the data are stored.
.Ease of hardware replacement - programmer would no longer alter a program when data should be migrated to newer model of storage device, provided it supports the same access methods.
.Easy shared data set access - an access method is a trusted program, that allows multiple programs to access the same file, while ensuring the basic data integrity.
