Editing Random-access machine (section)

{{Short description|Abstract machine in the general class of register machines}}
{{Distinguish|Random-access memory|text=[[Random-access memory]]}}
{{Multiple issues|{{More footnotes needed|date=December 2017}}{{Technical|date=December 2017}}{{Tone|date=December 2017}}}}

In [[computer science]], '''random-access machine''' ('''RAM''' or '''RA-machine''') is a [[model of computation]] that describes an [[abstract machine]] in the general class of [[register machine]]s. The RA-machine is very similar to the [[counter machine]] but with the added capability of 'indirect addressing' of its registers. The 'registers' are intuitively equivalent to [[Random-access memory|main memory]] of a common computer, except for the additional ability of registers to store natural numbers of any size. Like the counter machine, the RA-machine contains the execution instructions in the finite-state portion of the machine (the so-called [[Harvard architecture]]).

The RA-machine's equivalent of the [[universal Turing machine]]{{spaced ndash}}with its [[Computer program|program]] in the registers as well as its data{{spaced ndash}}is called the [[random-access stored-program machine]] or RASP-machine. It is an example of the so-called [[von Neumann architecture]] and is closest to the common notion of a [[computer]].

Together with the [[Turing machine]] and [[counter-machine model]]s, the RA-machine and RASP-machine models are used for [[computational complexity analysis]]. Van Emde Boas (1990) calls these three together with the [[pointer machine]], "sequential machine" models, to distinguish them from "[[parallel random-access machine]]" models.