Random access
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2008-07-12T00:29:59Z
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[[Image:Random vs sequential access.svg|thumb|right|Random access compared to [[sequential access]].]]
In [[computer science]], '''random access''' (sometimes called '''direct access''') is the ability to access an arbitrary element of a [[sequence (mathematics)|sequence]] in equal time. The opposite is [[sequential access]], where a remote element takes longer time to access. A typical illustration of this distinction is to compare an ancient [[scroll (parchment)|scroll]] (sequential; all material prior to the data needed must be unrolled) and the [[book]] (random: can be immediately flipped open to any random [[page]]. A more modern example is a cassette tape (sequential—you have to fast-forward through earlier songs to get to later ones) and a compact disc (random access—you can jump right to the track you want). The term [[random access memory]] (RAM), however, is used for semiconductor chip memory circuits used in computers. (The term was also used to describe [[ferrite-core memory]] in early computers).
In [[data structure]]s, random access implies the ability to access the ''N''th entry in a list of numbers in constant time. Very few data structures can guarantee this, other than [[array]]s (and related structures like [[dynamic array]]s). Random access is critical to many algorithms such as [[quicksort]] and [[binary search]]. Other data structures, such as [[linked list]]s, sacrifice random access to make for efficient inserts, deletes, or searches.
[[Category:Computer data]]
[[de:Wahlfreier Zugriff]]
[[es:Acceso aleatorio]]
[[fr:Accès direct]]
[[he:גישה ישירה]]
[[hu:Véletlen elérés]]
[[ja:ランダムアクセス]]
[[pt:Acesso aleatório]]
[[zh:隨機存取]]