Different File Type from Storage point of view
by Mohan[ Edit ] 2012-09-21 23:13:53
<h2>Different File Type from Storage point of view</h2>
File organization is a technique for storing and arranging data on secondary storage devices so that it can be retrieved easily when needed. It includes the physical order and layout of records on secondary storage devices. The techniques used to write and retrieve data to and from the storage devices called it access methods.
There are main three type of files from storage point of view.
Sequential files
Direct or random files
Indexed sequential file
Sequential Files
In sequential data files, records are stored on the storage media in a sequence. No locations are specified for individual records. The records are stored in an order, one after the other. Similarly, records are also retrieved in sequential order. It means that records are accessed one after the other in the same sequence in which they are stored on the storages devices. For example, to access a particular record from a data file, all records are searched one by one until the specified record in found. Therefore, accessing records in sequential files is very slow.
Direct or Random files
Direct files are also referred to as random files. In these files, records are not stored in a sequence. Each record is stored by specifying a particular address or location within a file. The address is calculated against the value of the key field of the record. Sometimes, the same address is calculated, which creates a problem to store record. This problem is known as synonym. Data accessing from direct files is very fast. A record is accessed directly by specifying its address.
Indexed Sequential Files
These files can be processed sequentially as well as randomly. In these files, the location of individual record is also stored along with data of record. For this purpose, an index is created to keep the track of locations of individual records.
Index refers to the location on the storage media where record is stored. You can say that an index is just like a table that is used to find out the location of a particular record. The key fields of the records are stored separately into the index along with the address of each record. Usually, an index is created in a new file called index file. The index file is updated whenever a new record is added or an existing record is deleted. Indexed file organization is more effective and fast in accessing data from data file than sequential file organization. These files occupy more space on the storage media but accessing speed of records is same as random access files.
