>>64bit VS will not buy you anything. Ultimate has more features.
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>>>I want to upgrade to Visual Studio 2013. Which one is the best: Visual Studio Professional 2013 or Visual Studio Ultimate 2013? I also understand there is no x64 version for that one. Is that correct?
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>Not questioning what you say other than to seek information on my understanding of what a 64bit program implies :
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>If you have a box with 16gb of RAM why wouldn't a 64bit version of VS use more of that RAM and less disk IO? Or are you saying this is an OS issue (the addressing of RAM beyound 3gb) and is not dependant on the program itself having a 64 bit address space?
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>If the latter, then 64bit SQL Server would be different because it is, in fact, a server and therefore is more like (part of) the OS in this regard?


Certain Windows Server versions can use up to 64GB of RAM in its 32-bit OS versions, but only 4GB of RAM per physical process. This is made possible by a hardware feature called PAE (Physical Address Extensions) which change the 32-bit address to a 36-bit address through tags in the paging tables. There are also unofficial patches for Windows Vista/7 which make those OS versions able to access beyond 4GB of physical RAM. And if you use an AMD processor, it increases even further beyond 64GB.

See: https://en.wikipedia.org/wiki/Physical_Address_Extension