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Sequential access is a term describing a group of elements (such as data in a memory array or adisk file or onmagnetic-tape data storage) being accessed in a predetermined, orderedsequence. It is the opposite ofrandom access, the ability to access an arbitrary element of a sequence as easily and efficiently as any other at any time.
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 all that is wanted is to process a sequence of data elements in order.[1]
There is no consistent definition incomputer science of sequential access or sequentiality.[2][3][4][5][6][7][8][9][improper synthesis?] In fact, different sequentiality definitions can lead to different sequentiality quantification results. In spatial dimension, request size, stride distance, backward accesses, re-accesses can affect sequentiality. For temporal sequentiality, characteristics such as multi-stream and inter-arrival time threshold has impact on the definition of sequentiality.[10]
Indata structures, a data structure is said to have sequential access if one can only visit the values it contains in one particular order.[11] The canonical example is thelinked list. Indexing into a list that has sequential access requiresO(n) time, wheren is the index. As a result, many algorithms such asquicksort andbinary search degenerate into bad algorithms that are even less efficient than their naive alternatives; these algorithms are impractical withoutrandom access. On the other hand, some algorithms, typically those that do not have index, require only sequential access, such asmergesort, and face no penalty.
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