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Random-access machine
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<p>In <a href="/facts/Computer_science/lN3pEyPz">computer science</a>, random-access machine (RAM or RA-machine) is a <a href="/facts/Model_of_computation/nJr8mHSI">model of computation</a> that describes an <a href="/facts/Abstract_machine/zuC4RKLn">abstract machine</a> in the general class of <a href="/facts/Register_machine/2SCc9Xof">register machines</a>. The RA-machine is very similar to the <a href="/facts/Counter_machine/FBxEgPld">counter machine</a> but with the added capability of 'indirect addressing' of its registers. The 'registers' are intuitively equivalent to <a href="/facts/Random-access_memory/DuD4bxh6">main memory</a> 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 <a href="/facts/Harvard_architecture/n9YMly7Q">Harvard architecture</a>). </p><p>The RA-machine's equivalent of the <a href="/facts/Universal_Turing_machine/2klpb1qQ">universal Turing machine</a> – with its <a href="/facts/Computer_program/e38jH9N9">program</a> in the registers as well as its data – is called the <a href="/facts/Random-access_stored-program_machine/5QuKq9BX">random-access stored-program machine</a> or RASP-machine. It is an example of the so-called <a href="/facts/Von_Neumann_architecture/te0yulFa">von Neumann architecture</a> and is closest to the common notion of a <a href="/facts/Computer/SQe1aK05">computer</a>. </p><p>Together with the <a href="/facts/Turing_machine/ojCtglYu">Turing machine</a> and <a href="/facts/Counter-machine_model/MwE2kwvV">counter-machine models</a>, the RA-machine and RASP-machine models are used for <a href="/facts/Computational_complexity_analysis/etHuVF3U">computational complexity analysis</a>. Van Emde Boas (1990) calls these three together with the <a href="/facts/Pointer_machine/0SdkYhF2">pointer machine</a>, "sequential machine" models, to distinguish them from "<a href="/facts/Parallel_random-access_machine/G1pCFgWP">parallel random-access machine</a>" models. </p>