>>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?

A 64-bit process may make use of more RAM than a 32-bit one. Whether it is designed to do so is another question. To avoid having 2 separate code bases the 64-bit version may just be a straight recompile of the 32-bit one.

If you have a box with 16GB RAM and you have a few GB free, Windows will use that for a disk cache. That cache may be large enough for most or all VS components that are used but not permanently memory resident.