Hi,

I recently purchased a 64 Bit AMD processor. All of my code (Fortran 77 and 90) has previously run on Unix and a windows machine. Is there anything I need to know about running on a 64 bit machine that is different to a 32 Bit machine? Do I need a different compiler?

If you have a compiled version of your code that runs under 32-bit x86, then it should be directly executable on the AMD chip, since the AMD chip is just a 64-bit x86 architecture. But in order to take advantage of the full 64 bits, you will need a compiler that ahs the capability to directly compile for the 64-bit x86 architecture.

nothing much i suppose ... the AMD processor is compatible with 32 bit as well, meaning, it will run your 32 bit binaries ... your 32 bit compiler will work but it won't produce 64 bit codes for you ... so you will need a new compiler to produce your 64 bit applications ... and make sure you link with the right libraries ... linking your 64 bit binary with 32 bit library will give you compilation error ...

sir, plz send me the code for the sub requested

err ... I don't understand whatcha meant ...

Tek Seang

As others have said, the 64-bit AMD processor can run 32-bit code with no penalty, but to make use of the extended addressing and additional instructions, you'll need a compiler capable of 64-bit compilation, e.g. Absoft Pro Fortran (version 8.5 or higher).

Personally I've not found any perfomance benefits of 64-bit executables over 32-bit executables. In fact they're slower in my application.

Others in my group have reported c. 30% speedup for their (3D CFD) application.

For AMD64, you can choose PGI, PathScale, Absoft Fortran compiler, and of course, you can also use free GNU g77 compiler. Here, I suggest PGI and PathScale compilers.

Even for completely same hardwares, the performance depends on OS, compiler, compiling option, your source code etc., therefore, we may have a different conclusion for the performance in 64 bit system and 32 bit system. I have got a better performance with 64 bit OS+Compiler rather than 32 bit OS+compiler in many of my tests, and there is also test case, which has almost same performance under 32 and 64 bit system.