64bit or 32 bit

Which should I install when I get my I get my software 64 or 32 bit Windows7. I have an E8400 proccessor and 4G ram. Dont know if thats enough info. Thanks Already running XP pro and plan to Use Windows 7 Pro retail on a second HDD.
May it's even depend on which kind of Application you'll run!

Let say you run only newer software 32 or even 64 bit, it could fine with 64 bit Windows. If you don't have any 64 bit applications, I would run 32 Bit Windows.

In case you also use old software like I did, use 32 bit Windows.

64 bit windows is able to run 32 bit applications. 32 bit Windows could run 16 bit software and even some 8 bit programs.

At the time a old 286 computer went down a few month ago, I use that machine for some CNC programming, I was stuck and just tested to start that program in Windows 7 Beta. I were able to get it to run in the DOS windows of Windows 7 which I even wasn't able to do in Windows 2000 or XP!! That's why I still run "just" the 32 bit version of Windows 7!

You'll need to choose what's the best for the application you'll run on your computer!.
Reimar, if he were to install Windows 32-bit, it would only use 3 (or so) of the installed 4GB.

To take full advantage of all the RAM that he purchased, he would need to use a 64-bit OS.
3.25 GB to be precise.

As I wrote, it's depend on which software he's using! With 4 GB of Memory Windows 7 64 bit isn't working as smooth as Windows 7 32 bit, special if he use 32 bit software/application only! Many programs, 32 bit I mean, would run in 32 bit environment better than in 64 bit environment. One example is for Games like the FS-X which runs much better on 32 bit Windows. Is the only Game I using and so I can tell just that from own experiences.

I learned with the time, that's not every time the best to have the "latest"! Many times the older is working better and faster without the need to change anything, to learn new procedures etc., etc.!
I have some legacy software which is 32 bit, but uses a 16 bit installer. Luckily I can install it on my 32bit XP and execute it from there, because, though it runs on my 64bit Vista and Seven, it can't install on either.
I also have 6Gb RAM, so I need 64bit architecture in the OS to avoid wasting half of it.
Remember 64bit OSs can run 32bit software, so they're the natural choice to future-proof your system.
Only stick with 32 bit if your hardware dictates it, or you are completely dependent on some very old apps which require 16bit support.
With 6 GB Memory I maybe would run the 64 bit version of Windows 7 but use Virtual Box or VM Ware for the older programs if I didn't have an other Computer!

For my own, my Main Computer has 16 GB Memory (OCZ 4 x 4 GB) and run 5 different OS': 1 Windows 7 64 bit; 1 Windows 7 32 bit; 1 Windows XP ; 1 Windows 2000 Server; 1 Ubuntu 10.04. Each OS has it's "own" HDD and I access the OS's using the BIOS Function for to choose the HDD which I want for to startup.
Mainly I use the 32 bit Windows 7 HDD and it is the fasted OS on that Computer.

Anyway, the choice of what to use is by each user and depending on what that user need to run or even like ti run. And Terry is right regarding the attached Hardware, if you didn't get 64 bit drivers you're on the lose!
I would say that windows 7 64-bit version is the best choicehttp://www.pcworld.com/businesscent...indows_7_upgrade_why_and_how.html?tk=rel_news. But as you have sufficient RAM 4GB, but I do not know that you have a supported m/b or devices that do supporting 64-bit drivers, or you need to upgrade an existing 32-bit installation, 32-bit Windows 7 might be the better choice. A few editions of 64-bit Windows 7 provide a http://www.infoworld.com/d/windows/windows-7s-xp-mode-right-idea-wrong-technology-171windows xp mode which is capable to solves some backward compatibility problems In speedy Quality and Assurance format.