Sequential access

In computer science sequential access means that a group of elements (i.e. data in a memory array or a disk file or on a tape) is accessed in a predetermined, ordered sequence. Sequential access is sometimes the only way of accessing the data, for example if it is on a tape. It may also be the access method of choice, for example if we simply want to process a sequence of data elements in order.

In data structures, a data structure is said to have sequential access if one can only visit the values it contains in one particular order. The canonical example is the linked list. Indexing into a list which has sequential access requires O( k ) time, where k is the index. As a result, many algorithms such as quicksort and binary search degenerate into bad algorithms that are even less efficient than their naïve alternatives; these algorithms are impractical without random access. On the other hand, some algorithms, typically those which don t perform indexing, require only sequential access, such as mergesort, and so face no penalty.

See also random access and direct access.