64 Bit is a the best version of Windows 7. It'll improve performance a lot as well, so I'm guessing gaming will be better too. Also 64 Bit is way more secure than 32 bit so your less prone to viruses and spy-ware as well. Also 32 bit cant handle anything more than 3 Gigabytes of ram, so with 64 bit, you can take full advantage of the 4 Gigabytes of ram you got there. Sounds like you have a really good PC, but its time to back up and pop in that 64x Bit Windows 7 PC. The move I went from 32 Vista Home Premium(YUCK!) -> 32 bit Windows 7 Ultimate(Incredible) ->64x Bit Windows 7 (Phenomenal!!!) It was amazing. Boot time takes about 20-30 seconds with a 4 Gigabyte, 1.83 (Ghz Dual Core Intel T5550 Centrino). So if I were you, go 64x bit BUT be sure that all your games and hardware are compatible (Which normally for most things after 2007 are).
Also here's the source were you can find your 64 bit and processor info: http://products.amd.com/en-ca/DesktopCPUDetail.aspx?id=506
MY PC INFO:
procesor: ADM athlon 7750 Dual-Core Processor, 2700 Mhz, 2 Cores, 2 Logical procesor (ADM Athlon X2 64)
Installed RAM: 4GB
Graphic Card: NVIDIA GeForce 9600 GT
HARD DRIVE: 600 GB (+ 1 TB (usb))
Gigabyte technology
Now im using Win 7 ultimate x32, i play a lots of games, i want to use my all 4 gb ram. and i have another quastion, how big improvment would it make on GAMES on x64 version...?
If you got any other quastions to me, just ask
!!!
Thanks to anyone who gonna anwser my quastion
!!!
Sorry for my bad english...

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