It depends how you define 20%. After bootup, my 64 bit installation uses approximately 20% more memory than my 32 bit install (although it isn't a fair comparison because the machines have different amounts of memory). However, a large amount of that is because windows requires loading of both 32 and 64 bit libraries. After the main libraries are loaded, unless something else requires both 32 and 64 libraries of the same thing for some reason, the memory usage shouldn't be all that much more. All data types are still the same size in 64 bit programs  (assuming you're comparing an indentically compiled program without different code paths for 32/64) except for pointers, which generally aren't going to add massive amount of memory usage.

As for 16 bit applications, DOSBox handles pretty much all of your needs (and in most cases you'd want to use DOSBox anyway under a 32 bit OS).

64-bit OSs:

- Allow you to fully use 4GB+ of memory

- Can only be run on AMD64 processors

- Use more memory in general

- 32-bit applications or unoptimised ones are generally slower

- Optimised 64-bit applications are generally faster

- Many driver incompatibilities at present: it can be difficult to make hardware work

Go into Control Panel and click on System. If you have SP1 it'll show up in the Windows edition section. You went with the best version of Vista. I heard of massive compatibility issues with the 64-bit version. I rather not deal with that right now and wait to go 64-bit for my next PC. It's bad enough to get some games running on Vista let alone another loophole...

XP 64 bit has never taken off, with all the driver issues and hardly anyone optimising for Vista 64 bit Id say your safest bet is to use 32.

I don't know where you got that from.

You might have heard of a small start up company called Intel? Any intel processor with EM64T extensions can run 64 bit  programs. Think core2 and even some of the cpus before that had it.

Yeah, Intel's Core 2 and later are AMD64 compatible. But AMD invented it and Intel cloned it.

Not like AMD never licensed intel technologies. Hello SSE!

Due to AMD and Intel's special situation (whereby AMD ought not to exist if it weren't for some questionable court cases) they have an agreement to freely use each others' technology after a set period of time. Both companies innovate, cross-license and then 'steal' (e.g. QPI = HyperTransport). I am choosing to call it AMD64, as many vendors call it x86-64, Intel 64 or EM64T:

"Since AMD64 and Intel 64 are substantially similar, many software and hardware products use one vendor-neutral term to indicate their support for both implementations. AMD's original designation for this processor architecture, "x86-64", is still sometimes used for this purpose, as is the variant "x86_64".^[13] Other companies, such as Microsoft and Sun Microsystems, use "x64" (as a contraction of "x86-64") in marketing material.

Many operating systems and products, especially those that introduced x86-64 support prior to Intel's entry into the market, use the term "AMD64" or "amd64" to refer to support for both AMD64 and Intel 64.

• BSD systems such as FreeBSD, NetBSD and OpenBSD support both AMD64 and Intel 64 under the architecture name "amd64".

• Debian GNU/Linux, ubuntu, and Gentoo support both AMD64 and Intel 64 under the architecture name "amd64".

• Java Development Kit (JDK): The name "amd64" is used in directory names containing x86-64 files.

• Microsoft Windows: x64 versions of Windows use the AMD64 moniker to designate various components which use 64-bit technology for IA-32 processors. For example, the system folder on a Windows x64 Edition installation CD-ROM is named "AMD64", in contrast to "i386" in 32-bit versions.

• Solaris: The isalist command in Sun's Solaris operating system identifies both AMD64- and Intel 64–based systems as "amd64"."

- Wikipedia

While I agree that XP64 was almost completely ignored by hardware vendors, MS requires vendors that get their vista drivers WHQL'd to provide 32 and 64 bit drivers. No guarentee you'll be able to get drivers for smaller vendors (ahem...Line 6, though they've just released drivers) or older hardware, but there are significantly more available for Vista 64 than there ever was for XP64.

Thanks. I seem to not have SP1 installed. Should I install it? I hear it fixes very little, and slows the OS down (sounds like Vista vs XP :p).

What do you guys think? :)

P.S. Thanks for the history lesson on AMD64. Very interesting.