88 research outputs found
Turing machines with access to history
AbstractWe study remembering Turing machines, that is Turing machines with the capability to access freely the history of their computations. These devices can detect in one step via the oracle mechanism whether the storage tapes have exactly the same contents at the moment of inquiry as at some past moment in the computation. The s(n)-space-bounded remembering Turing machines are shown to be able to recognize exactly the languages in the time-complexity class determined by bounds exponential in s(n). This is proved for deterministic, non-deterministic, and alternating Turing machines
Deterministic Computations on a PRAM with Static Processor and Memory Faults.
We consider Parallel Random Access Machine (PRAM) which has some processors
and memory cells faulty. The faults considered are static, i.e., once the
machine starts to operate, the operational/faulty status of PRAM components
does not change. We develop a deterministic simulation of a fully operational
PRAM on a similar faulty machine which has constant fractions of faults among
processors and memory cells. The simulating PRAM has processors and
memory cells, and simulates a PRAM with processors and a constant fraction
of memory cells. The simulation is in two phases: it starts with
preprocessing, which is followed by the simulation proper performed in a
step-by-step fashion. Preprocessing is performed in time . The slowdown of a step-by-step part of the simulation is
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