Some people that try to explain 64 bit performance will simply say “64 bit is faster”. That is incorrect. Though the actual results may make that appear to be accurate.
Think of your computer as a multi lane highway. The I/O path (Processor, System bus and RAM) limit the number of lanes (32 or 64bit) of traffic. The bits are represented by cars. The objective is to get the most cars moving at the same time.
All new processors, Intel or AMD, sold as new today are 64 bit capable. All new memory is 64 bit capable also. Most new motherboards are 64 bit capable as well.
Using a 64 bit operating system does not increase the speed limit of the highway, it increases the lanes from 32 to 64. The Ghz rating of your Processor is the speed limit of the highway.
The hard drive is like a Long Term Parking lot. Cars can NOT move fast in the long term parking lot, but they can be stored efficiently there.
The RAM is like an On ramp and Off ramp that offers 64 lanes on and off of the highway.
Now 64 cars (bits of information) can be moved at once.
If you are only using one application to do a small amount of work, the lanes will not get congested with 32 bit. When you attempt to run several applications like Firefox and Photoshop and Adobe Acrobat all at the same time the 32 lane highway becomes congested and everything goes slower than the posted speed limit. On a 64 bit operating system this is less likely to happen, it also happens less often. The number of lanes prevents the traffic jam from building up in the first place.
Ultimately more data is moved at the same time resulting in better performance, when more lanes are in use. I will post part two about multiple cores and symmetric multi processing soon.
An interesting note: Adobe Photoshop was originally created by Adobe on and for MacIntosh computers. Adobe has released a 64 bit version of Photoshop for 64 bit versions of Windows but has not released a 64 bit version for 64 bit Mac OS.