Sequential access is the reading or writing of 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.
Sequential Access in Programming
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.
Other Sequential Classifications
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.
Recommended Reading: Webopedia’s random access definition.