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I can confirm Kevin's and Kay's comments. The distributed Linux and Windows 32-bit binaries of SHELX are compiled with the Intel compiler and there appears to be no significant performance gain to be achieved by recompiling them as 64-bit (even for an AMD machine), so I have no plans to distribute 64-bit versions.
The only exception is that if you wish to do full-matrix refinement using SHELXL with more than about 32765 parameters you will need to use a 64-bit CPU and OS, and change the dimensions as explained in the source and recompile for 64-bits because 64-bit integer arithmetic will be needed for the array addressing (and then you will also need more than 2GB RAM, otherwise it runs in disk excerciser mode).
George -- Prof. George M. Sheldrick FRS Dept. Structural Chemistry, University of Goettingen, Tammannstr. 4, D37077 Goettingen, Germany Tel. +49-551-39-3021 or -3068 Fax. +49-551-39-2582
