For servers, 64-bits will be quite a painful one. Lots of applications out there (especially PHP) will require tons of libraries in 32 bit. Since most of your libraries will be in the 64-bit library, you will need to work out the configuration and do some manual symbolic links to the normal path PHP will find.

IMO, you should not be getting 64-bit unless your gonna do the easy (apt-get, yum) way.

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