If your system won't plan to add the system more than 4GB Memory it is no point to use x64 Windows. Still now some software is still not support 64 Bit system. Windows 7 x64 also use a little bit more RAM than x86. Detail depends on your system detail (like if any high grade display and if you put any system memory for shared memory for your graphic board etc.
If you can add the extra 2GB do it (read your motherboard manual).
1) 2GB -> 32-bit Windows
2) 3GB or 4GB -> 64-bit Windows
There are other advantages to 64-bit. Software compatibility and drivers are generally a non-issue but double check.
64-bit is the future. Windows 8 is confirmed to be 64-bit only but that's not a reason to switch now.
There is generally no performance advantage to 64-bit as 99.9% of programs are actually running on 64-bit Windows in a 32-bit emulation mode. 64-bit programs are starting to appear though, but it's likely we won't see a huge surge until Windows 8 approaches in 3 years.
If you have 4gb, then by all means install the 64bit version of vista or windows-7. It is a more secure OS and it will let you use more of your 4gb. A 32 bit OS will see only about 3.4gb.
It is true that 64 bit vista or windows-7 will use more ram. That is a good thing. XP was built when ram was expensive. It therefore does much extra work with the page file to conserve ram. Vista, on the other hand uses ram to cache useful data so that it does not have to retrieve it from the hard drive. You can consider that XP wastes ram by not using it.
If you run 32-bit software in a 64-bit environment it will use twice as much memory. As a 64-bit OS uses 64-bit words, when you run a 32-bit program, there is some emulation of course, the OS reserves 64 bits for every 32-bit word that the application is using. An app that would use 20MB in a 32-bit OS would use 40MB in a 64-bit OS (even though it was technically only using half of that the OS would reserve 40 for it).
The rate isn't exactly double as some parts of the app are native windows code (make the window, buttons, help, etc.), but the memory that the app is reserving itself(it's variables) would take up twice as much space.
Not exactly true. Whether you have 1GB, 2GB, 4GB or 32GB... 64-bit Windows will run just fine. The increase is more like 25% rather than 100%. The main reason for this is because Windows must load 32-bit and 64-bit libraries when running 32-bit programs under x64. The programs themselves do not consume any more RAM than they normally would under x86. Each program is allocated 2GB of address space... regardless of how much it actually uses.
Each program is allocated 2GB of address space... regardless of how much it actually uses.
Just to clarify - each 32-bit program has access to 2GB of virtual space. Programs that don't need 2GB of space won't actually use 2GB of physical RAM, and even a program that uses 2GB of virtual space will run (albeit slowly) on a system with only 1GB of memory because the overflow is put into the page file.
I installed Windows 7 x64 on my computer without knowing it was 32-bits... what will happen to my computer? I just clicked on x64 thinking it was smaller than x86, so should I just reinstal it or am I fine like this and just need to upgrade my computer a little?
Since this thread was brought back to life, I would like to correct this statement
"If you run 32-bit software in a 64-bit environment it will use twice as much memory. As a 64-bit OS uses 64-bit words, when you run a 32-bit program, there is some emulation of course, the OS reserves 64 bits for every 32-bit word that the application is using. An app that would use 20MB in a 32-bit OS would use 40MB in a 64-bit OS"
The only thing that's forced from 32bit to 64bit is memory pointers.
Lets say you have an array of data that's 128k in size. You need a pointer to "point" to the location in memory where this array is. In a 32bit machine, this pointer would consume 32bits, in a 64bit machine, it would be 64bits, but the actual data is still 128K.