Random Access Machine

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See: RAM, Abstract Machine, Register Machine, External Memory Model.



  • http://en.wikipedia.org/wiki/Random_Access_Machine
  • (Schweikardt, 2009) Nicole Schweikardt. (2009). “Machine Models for Query Processing.” In: SIGMOD Record, 38(2).
    • In the classical random access machine (RAM) model, the input consists of N data items, each of which can be represented by a bitstring of length O(logN). An unbounded number of data items can be stored in memory. Access to any item in memory as well as arithmetics and bitwise operations on data items can be performed in constant time.
    • The basic external memory model (cf., e.g., [27]) can be viewed as a refinement of the RAM model where memory is divided into internal memory, capable of storing up to M data items, and external memory of unbounded size. Data present in internal memory can be accessed quickly (as in the RAM model). Data present in external memory can only be accessed by an operation called Input/Output communication (I/O, for short) that moves a contiguous block of B data items between internal and external memory. Initially, the N input items are stored in external memory. One typically assumes that M < N and 1 6 B 6 M/2.