Customers installing Windows on their Macs often ask whether they should go with a 32 or 64-bit version of Windows (Win32 or Win64). All Macs made after 2006 are using a 64-bit processor (Core 2 Duo, Xeon, i5 or i7), so the assumption is that a 64-bit version of Windows would be the best choice. There’s more to it than that.
With Mac OS X, 32 and 64-bit modes are provided with one install (assuming your system supports it—a Core Duo does not run in 64-bit mode but a Core 2 Duo can). If your system has a 64-bit processor, then OS X can start in 64-bit mode and support 64-bit applications. Windows, on the other hand, comes in 32 or 64-bit versions, which are not always sold together in the same package. Further, a different set of hardware drivers is required for each flavor. 32-bit drivers do not work with Win64, so if the manufacturer of a peripheral didn’t bother to supply a 64-bit driver for it, the device may not work properly. Windows often has basic support for multimedia hardware, but some features may not be available. (Microsoft has updated their logo program, so any device that says “Compatible with Windows 7” has been tested to be functional with both the 32 and 64-bit versions.)
Basically, these are the questions to ask yourself:
Do I need to run any 64-bit applications?
If not, then there’s really no reason to run Win64. One example is Excel: the advantage of the 64-bit version is that it can handle very large files, but if you just do the occasional home-budget type spreadsheet, then you will be fine with the 32-bit version. Still, you may want to install Win64 anyway, in case you do need a 64-bit app in the future. Sometimes it’s nicer to have a feature and not need it than it is to need it and not have it.
Do I have any devices that do not support 64-bit?
Check the compatibility of any external hardware, such as scanners; if they do not list 64-bit drivers, then they will not work with Win64. The device may work fine using Mac OS, but Windows will not recognize it, so you would have to scan in the document using a Mac application, then share the document with Windows. While this works fine for the occasional scan, if you need to do a LOT of scanning under Windows, then you need the 32-bit version of Windows for driver support.
What kind of system am I installing it to?
This is the most important one. Both the 32 and 64-bit versions of Windows 7 will run in 2GB of RAM, but the Win64 version running 64-bit applications really does not show dramatic performance gains unless you can dedicate at least 4GB to it. Using a program like Parallels or VMWare Fusion will let you run Windows within Mac OS X, but your RAM is shared between them. If your Mac only has 4GB RAM total, you can only (at best) dedicate 2GB to the Windows side. In this case, your best option is to either use the Win32 version in Parallels, or install Win64 in Boot Camp so Windows can take full advantage of the available memory. It means having to reboot every time you need one OS or the other, but you’ll have better performance in each one. If you have 8GB or more, you can dedicate the required 4GB to the Windows side within Parallels.
For comparison, here are RAM breakdowns for each system:
MacBook Air: Older models support 2GB, newer systems can support 4GB. (The MacBook Air is not upgradable.)
MacBook / MacBook Pro: Original style 2008 and 2009 models can support 6GB. Pre-2011 unibody systems can support 8GB. The 2011 MacBook Pro line can support up to 16GB.
iMac: Depending on the year and model, it can support anywhere from 4GB to 32GB.
Mac mini: 2009 and 2010 versions can support 8GB. The 2011 model can use 16GB.
Mac Pro: From 16GB to 64GB depending on the model.