[Beowulf] g77 limits...

Robert G. Brown rgb at phy.duke.edu
Wed Feb 22 14:24:33 EST 2006

Dear List,

What are the current limits on the size of arrays that can be allocated
in g77?  I know that this is almost a FAQ, but I cannot look back at the
archives because it is so time dependent an answer.  In particular, can
an x64 box with a modern linux kernel and a modern g77 allocate 4-8 GB
arrays (presuming, of course, that one uses a long int for an index)?  I
have seen references to "using an offset" in a few google hits (that
were not very informative) -- does that basically mean doing pointer
arithmetic in fortran?

I ask because:

   a) I'm not a fortran expert -- in fact the last time I >>willingly<<
coded in fortran was twenty or so years ago.

   b) Alas, I'm probably going to have to become one (again).

   c) Working on some problems with potentially very large memory

   d) Where commercial compilers aren't a viable option (although I
suggested them) -- the software has to build and be usable by e.g.
researchers in countries where there simply is no money to spend on

The last suggests that it would be ideal if large arrays were at least
approximately "transparent" -- so that the software would build on 32
bit systems and be runnable there with smaller arrays but would also
build and run on x64 big-memory systems without the need for extensive
instrumentation of the code.



(I know Toone works on this and am hoping he's paying attention so I can
get a really authoritative and informative answer...:-)

Robert G. Brown	                       http://www.phy.duke.edu/~rgb/
Duke University Dept. of Physics, Box 90305
Durham, N.C. 27708-0305
Phone: 1-919-660-2567  Fax: 919-660-2525     email:rgb at phy.duke.edu

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