file access

In computing, the way in which the records in a file are stored, retrieved, or updated by computer. There are four main types of file organization, each of which allows a different form of access to the records: serial file, sequential file, indexed sequential file, and direct-access (or random-access) file.

Records in a serial file are not stored in any particular order, so a specific record can be accessed only by reading through all the previous records.

Records in a sequential file are sorted by reference to a key field (see sorting) and the computer can use a searching technique, such as a binary search, to access a specific record.

An indexed sequential file possesses an index that records the position of each block of records and is created and updated with that file. By consulting the index, the computer can obtain the address of the block containing the required record, and search just that block rather than the whole file.

A direct-access or random-access file contains records that can be accessed directly by the computer.