A very common question that is asked by CAD users is, "Is 64 bit is better for CAD?". I think much of this stems from the amount of focus the market has put on the 64 bit computing and maybe the fact that the number 64 is twice that of 32 which implies it MUST be better. However the trends suggest that mileage does vary depending on the type of software, hardware and operations the system endures.
There are, however, some prerequisites that have to be met first with the hardware of the system before a 64 bit operating system is to be considered. The most important factor is the CPU, which will need to be 64 bit capable. Many systems today will support an installation of Windows 64 (Either XP, Vista or Windows7 (currently in Beta)), but the other factor is RAM. If your system is not equipped with at least 4GB of RAM or more then the reasons for migrating to this platform diminish dramatically. Placing 4GB or more on a system and will require the motherboard of the system to also be able to support this type of configuration as well. Now I have only highlighted the main hardware prerequisites however there are some specific hardware requirements in order for all 32 bit applications to utilize the 64 bit environment by accessing WOW64. I won't be diving into that topic here.
Once the hardware specific requirements are met, the installation procedure is essentially the same as it's 32 bit counterpart. So let's assume you have 8GB of RAM on your system and now running 64 bit Vista, what have you gained? There are essentially two benefits to running a 64 bit OS. One, 64 bit specific applications have access to 64 bit processing, which means that the CPU can process twice as much information than 32 bit. However when it comes to CAD this tends to not be that beneficial although there are some analysis applications that can take full advantage of 64 bit processing. Two, it's all about RAM. As you may know 32 bit Windows can only address 4GB of RAM, which by default is shared 50/50 between the operating system and applications. You can enable the 3GB switch which is a boot level configuration to override this split for system that have 4GB of RAM to give 3GB to the application space. With 64 bit, Windows can address up to 128GB of RAM which is where all the performance gain resides.
Being able to address more RAM allows the CAD application to load and work entirely in RAM. This allows operations to be performed on top-level large assemblies than might have not been able to even be opened in a 32 bit environment. This prevents using virtual RAM, better known as the paging file in Windows, which is hard drive space. Once a program accesses the paging file, performance tends to dip dramatically. With that being said, the 64 bit environment is really only beneficial to those who come up on the 3GB ceiling and are running RAM intensive programs like CAD, photo/video editing or gaming.
Now obviously not all the applications you have are 64 bit so compatibility with your 32 bit applications is also a key part to your decision to switch to 64 bit. When I first used Windows XP x64 back in 2005/2006 it was pretty painful since many of my peripherals (XEROX printer) and speciality programs were not yet supported. Today Vista-64 and Windows7-64 (beta) are more mature and much more forgiving to run 32 bit applications then XP-64 was in it's early days.
The biggest challenge seems to still be hardware drivers. When Vista first shipped, many consumers were having issues getting video cards to support the new Aero graphics and some other legacy hardware to work. 64 bit for Vista and Windows7 seem to have corrected the compatability issues but they do require signed drivers. If you have any hardware that does not have Microsoft signed drivers, that hardware will not install and this can add some pain depending on your setup.
Overall if your CAD requirements involve large assemblies, large feature-count parts or you have multiple memmory-resident programs you want to run simultaniously, 64 bit is probably for you. Performance gain can be quite dramatic for these types of applicatoins but common tasks like word processing, spreadsheets and browsing the internet will run as they do currently in 32 bit Windows. 64 bit is migrating over to be the standard and is much easier of a transition with new hardware. I am currently testing Windows7 x64 and will be back shortly to share that experience with you! ~Lou