ACCESS METHODS IN FILE SYSTEM


Files are used to store data. The information present in the file can be accessed by various methods.

The way of retrieving data from a file is known as Access Method

The various Access Methods are as follows:

§  Sequential Access Method

§  Direct Access Method

§  Indexed Access Method

Sequential Access Method:

§  It is the simplest and most commonly used access method.

§  In Sequential Access, records are accessed in some sequence i.e. the information in the file is processed in order, one record after the other.

§  The various records are read sequentially one after the other in an order, starting at the beginning to the end of the file.

§  The various records cannot be read randomly out of order that we cannot skip any record in between.

§  For example: Reading of 34th record followed by 5th record and then 1st record is not possible in sequential access.

§  Sequential File can be reset to the starting of the file.

§  Sequential access is convenient when the storage medium is magnetic tape rather than a disk.

Direct Access Method:

§  In Direct Access Method, it is possible to access the records of a file in any order.

§  For Example: if we are reading block 13, then we can read block 44 and then can read block 29.

§  The various records can be read or write randomly.

§  There is no restriction on the order of reading or writing for a direct access file.

§  The records can be accessed by key, rather than by position.

§  This method is used in systems implementing disks rather than magnetic tapes.

§  This method is important for many applications, for example: database systems.

§  In banking application, a customer may want to look up his current balance.

§  This can be done by account number of customer as a key. Rather than sequential reading the records for thousands of customers.

Indexed Access Method:

§  In this method, an Index is created for the file.

§  This index contains pointer for various blocks of a file just like an Index in the book.

§  If we want to find a record of a file, first the index is searched and then the pointer from index is used to access that file.

§  In this way, A Required Record is found.

§  Index is searched sequentially and its pointer is used to access the file directly

Advertisements

Give A message for us

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s