Which access method is least efficient for data retrieval?

Answer Details

Access methods describe how a computer locates and retrieves a specific record of data from storage, and their efficiency depends on whether every record must be checked along the way.

Sequential access requires the storage device to read through records one after another, in order, starting from the beginning, until the required record is reached. To retrieve a record located near the end of the file, every preceding record must first be read and passed over, which makes this method comparatively slow, especially for large files or when the required record is far from the start. Magnetic tape is a classic example of a storage medium that only supports sequential access.

The other access methods are all designed to reach a specific record more directly. Direct access (also called random access) allows the storage device to move straight to the physical location of the required record without reading through the ones before it. Indexed access uses a separate index that maps each record to its location, allowing the system to look up the index first and then jump directly to the record, combining fast lookup with organised storage. Random access is effectively the same principle as direct access, retrieving any record directly regardless of its position.

When a question asks which method is "least efficient" for retrieval, look for the one that must pass through preceding records in order, since sequential access is the only one listed that cannot jump directly to the required data.