But, tacit's statement also says, and perhaps I was mislead by, "If you don't have more than 4 GB of RAM installed in your system, then it'll make no difference." (Emphasis added)
Far be it from me to argue with Tacit's assertions, but FWIW my test results belie his claim. My system with only 4GB of RAM actually shows performance improvements in every area except CPU speed when running in 64 bit mode with a surprising 18% improvement in hard drive performance. I will let you draw your own conclusion from that.
So our readings reflect coding (Right word?), rather than functionality, differences, i.e. the fact that our apps appear to be running in 64-bit mode is no more than an illusion as far as performance goes.
If by "coding" you mean that data storage is allocated in 64 bit "words" rather than 32 bit "word" where a "word" is an addressable unit of virtual or real memory that is correct. However, since my test results show an actual improvement in performance running in full 64 bit mode I have to question your use of the word
illusion. It is pretty substantial to be called an illution.
In conclusion, then, as apps are upgraded it will pay users to ensure that they are not running in their 64-bit incarnations if the Macs on which they are installed cannot run in 64-bit mode, because they will be needlessly hogging system resources.
Whether the additional memory resources are
needlessly hogging system resources or not is open to question and experimentation. Until tests are conducted, on an app by app basis, that is pure speculation. It may well be the apps run faster and/or more efficiently in one mode or the other.
It may well be the next generation of Intel CPUs and the myriad of support chips before the benefits of 64 bit mode can be fully realized. It will definitely require a new generation of applications written specifically to take advantage of the additional memory space and other processing advantages. But before any of that can effectively be utilized the full 64 bit capabilities of the Snow Leopard kernel has to be in place. Snow Leopard is merely one step on the journey, but it is a
big and
very important step.