On Tue, 08 Oct 2013 10:46:50 +0530, Ravi Sahni wrote: > On Tue, Oct 8, 2013 at 8:47 AM, rusi <rustompm...@gmail.com> wrote: >> I can only say how ironic it sounds to someone who is familiar with the >> history of our field: Turing was not a computer scientist (the term did >> not exist then) but a mathematician. And his major contribution was to >> create a form of argument so much more rigorous than what erstwhile >> mathematicians were used to that he was justified in calling that math >> as a machine. >> >> The irony is that today's generation assumes that 'some-machine' >> implies its something like 'Intel-machine'. To get out of this >> confusion ask yourself: Is it finite or infinite? If the TM were finite >> it would be a DFA If the Intel-machine (and like) were infinite they >> would need to exist in a different universe. > > With due respect Sir, you saying that Turing machine not a machine? Very > confusion Sir!!!
The mathematical ideal Turing Machine has an infinitely long tape, equivalent to infinite memory, and may take an unbounded amount of time to complete the computation. Since no *actual* physical machine can be infinitely big, and in practice there are strict limits on how long we are willing to wait for a computation to complete, in the *literal* sense, Turing Machines are not *actual* machines. They are a mathematical abstraction. But in practice, we can wave our hands and ignore this fact, and consider only not-quite-Turing Machines with finite amounts of tape, and note that they are equivalent to physical machines with finite amounts of memory. One could even build such a finite Turing Machine, although of course it would be very slow. Or one can simulate it in software. So in that sense, computers are Turing Machines. Anything a physical computing device can compute, a Turing Machine could too. The converse is not true though: a Turing Machine with infinite tape can compute things where a real physical device would run out of memory, although it might take longer than anyone is willing to wait. -- Steven -- https://mail.python.org/mailman/listinfo/python-list
