Refers to reading or writing data records in sequential order, that is, one record after the other. To read record 10, for example, you would first need to read records 1 through 9. This differs from random access, in which you can read and write records in any order.
Some programming languages and operating systems distinguish between sequential-access data files and random-access data files, allowing you to choose between the two types. Sequential-access files are faster if you always access records in the same order. Random-access files are faster if you need to read or write records in a random order.
Devices can also be classified as sequential access or random access. For example, a tape drive is a sequential-access device because to get to point q on the tape, the drive needs to pass through points a through p. A disk drive, on the other hand, is a random-access device because the drive can access any point on the disk without passing through all intervening points.