In my (SHELX) experience, the difference in performance between 32bit and 64bit versions running on a 64bit OS scarcely justifies distributing two sets of binaries. The 64bit binaries are usually slightly faster (especially the multi-CPU SHELXD). As far as I know, there are no problems running the 32bit SHELX binaries on a 64bit system (zero dependencies again!). There is however one exception: for full-matrix SHELXL refinements with a large number of parameters, the matrix can be too large for 32bit addressing.
George On Thu, Sep 01, 2011 at 11:36:21AM -0700, Ethan Merritt wrote: > On Thursday, September 01, 2011 11:02:50 am Ed Pozharski wrote: > > I am almost sure this has been addressed before, so you can go after me > > for insufficient googling. However, > > > > 1. Is there any *significant* advantage in using 64-bit CCP4 binaries > > (primarily speed)? > > 2. IIUC, the standard CCP4 download results in 32-bit binaries being > > run on a 64-bit system. Works for me (except for the weird iMosflm > > issue), but given that 64-bit OS is becoming more and more common, isn't > > it time for 64-bit binaries option? The answer, of course, is no if you > > answered no to 1 above. > > The generic answer is that there is no intrinsic speed advantage to running > a 64-bit binary rather than a 32-bit binary. In fact it may run slower > due to larger pointer sizes and hence poorer cache performance. > However, 32-bit binaries cannot access more than 4GB of address space. > > But the x64 architecture provides more registers and faster instructions > than x86. So a 32-bit binary using the x64 instruction set can run faster > than a 32-bit binary using only x86 instructions. Therefore you need to > choose the right compiler options in order to get the benefit of the faster > architecture. > > I do not know if there are specific CCP4 programs that fall outside of > the generic case described above. > > Ethan > > -- > Ethan A Merritt > Biomolecular Structure Center, K-428 Health Sciences Bldg > University of Washington, Seattle 98195-7742 > -- Prof. George M. Sheldrick FRS Dept. Structural Chemistry, University of Goettingen, Tammannstr. 4, D37077 Goettingen, Germany Tel. +49-551-39-3021 or -3068 Fax. +49-551-39-22582
