When we access the data inside the file, it needs to be read into the memory before further execution is done. There are certain ways in which the information inside a file can be accessed.
Different methods of file access in the operating system are given below:
This is the most common file access method. The information in the file is processed in order, one record after the other. All the information needs to be loaded sequentially for random access inside the given file. Usually, it contains read, write and rewind file operations.
The read operation (read next) reads the data stored on the next position of the pointer and moves the pointer forward by one read point. The write operation (write next) adds the data at the end of the file and moves the pointer forward to the newly written data. The rewind operation moves the pointer backward until the file's required information appears. An example of this file access method can be accessing data from a tape.
This method is also known as the relative access method. A file is composed of fixed-length logical records called blocks. These blocks can be accessed in any order. The file is accessed as a numbered sequence of blocks or records. Therefore, we may read block 10, then read block 40, and then write block 5.
There are no constraints on the order of reading or writing for a direct-access file. Direct access files are of great use for intermediate access to large amounts of information, and most databases are based on this type of file access.
A direct-access method serves as the foundation for this file access technique. An index is created for the entire file, which contains pointers to the various blocks inside the disk. To find a record in the file, we first traverse through the index and then use the pointer to access the file directly. However, in this file access, extra memory is required for keeping the index file, which burdens the memory resources.
The following shows the index file and how it works:
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