Anyways, you guys seem to complicate things which shouldn't be made "complicated."
Now here is my opinion.
I probably have the weakest Core 2 Duo T5500 laptop with only 1GB RAM and only Intel GMA 950 graphics. Windows XP will be better for me than Windows 7 in gaming and also in running more softwares at once because Windows XP has lower memory footprint than Windows 7 AND it will matter to me cuz I have only 1GB of RAM.
But when you have a capable system, there will be hardly any difference in the gaming performance between both the Operating Systems and Windows 7 might be faster.
In a nutshell, 1GB Windows XP vs 1GB Windows 7. Windows XP wins cuz Windows 7 uses more RAM at stock. 2GB Windows XP vs 2GB Windows 7 - hardly any noticeable difference as far as I am concerned. 3GB RAM or moe - use Windows XP if you still like it.
Now 32bit vs 64bit scenario.
32bit operating systems can't utilize RAM more than 4GB. 32bit processors handle 32bit wide integers whereas 64bit processors handle 64bit wide integers. There is hardly any performance difference between 32bit and 64bit tbh.
You have 1GB RAM. Try to limit yourself to Windows 32bit only. You have 2GB RAM, consider Windows 64bit. You have 3GB RAM or more, forget Windows 32bit. You have 4GB RAM, use Windows 64bit.
That is the way how I look at things.
I use Windows 7 32bit and Ubuntu amd64 in my laptop. The latter is my choice because I think it is the time to move on from 32bit Linux.
Last questions.
What about Windows Vista? It sucks.
What about Windows XP x64, I heard it exists? Has many compatibility issues.
Any compatibility issues in Windows 7 64bit? Almost zero as far as my usage is concerned. Runs my 32bit programs seamlessly.
Enough of crap, just tell me why 64bit? Time to move on.
32bit and 64bit drivers are different.
Nothing wrong in using 64bit OS in 1GB RAM or even 256MB RAM though.
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More information.
x86 is the family instruction sets developed by Intel which they used in their 8bit, 16bit and 32bit processors.
When Intel developed their 64bit processor named Itanium, they wanted to deviate away from x86 to
IA-64 which was significantly different from x86.
AMD didn't want to do that, they created
amd64 or
x86-64 which was an extension to x86 and fully backward compatible with 32bit too. (In today's world, x86 refers to 32bit) Intel had to give in and accepted x86-64. Although they called it EM64T and finally Intel 64.
AMD has shipped 64bit processors since 2003 with their Athlon 64.
And basically, amd64 is the reason why you guys can still use Windows 7 32bit or any other 32bit OS on your "64bit" processors seamlessly today.
In a nutshell,
x86-64 = amd64 = EM64T/Intel 64.
One question,
Can I install Ubuntu amd64 on my Intel Core 2 Duo E8400? Like I said, x86-64 = amd64 = EM64T/Intel 64. So, YES YOU CAN. Ubuntu calls it amd64, it is their decision.