Are parallel machines always faster than sequential machines?

Preliminary version
  • Louis Mak
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 775)


We demonstrate that parallel machines are always faster than sequential machines for a wide range of machine models, including tree Turing machine (TM), multidimensional TM, log-cost random access machine (RAM), and unit-cost RAM. More precisely, we show that every sequential machine M (in the above list) that runs in time T can be sped up by a parallel version M′ of M that runs in time o(T). All previous speedup results either rely on the severe limitation on the storage structure of M (e.g., M is a TM with linear tapes) or require that M′ has a more versatile storage structure than M (e.g., M′ is a parallel RAM (PRAM), and M is a TM with linear tapes). It is unclear whether it is the parallelism, or the restriction on the storage structures, or the combination of both that realizes such speedup. We remove all the above restrictions on storage structures in previous results. We present speedup theorems where both M and M′ use the same kind of storage medium, which is not linear tapes. Thus, we prove conclusively that parallelism alone suffices to achieve the speedup.


Parallel Machine Turing Machine Global Memory Machine Model Sequential Machine 
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Copyright information

© Springer-Verlag Berlin Heidelberg 1994

Authors and Affiliations

  • Louis Mak
    • 1
  1. 1.University of Illinois at Urbana-ChampaignUrbanaUSA

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