Originally Posted by Brian Green
Solipsism, all I know is that I'm unable to boot into 64 bit mode because of the EFI chip being 32 bit. If Apple is going to make 10.7 a 64 bit cat, I'm going to be having to recycle my Mac Pro for a new one. I'm hoping Apple issues an update that corrects this. Otherwise, there are a lot of people out here with 64 bit CPU's that won't boot the 64 bit kernel simply because of the EFI limitation and will be forced to recycle perfectly good and powerful Mac's or never update beyond Snow Leopard.
It is annoying that Apple refuses to get us this update in Snow Leopard, so hopefully they will in 10.7. I guess this is an excellent example of "planned obsolescence".
There are some benefits to moving to a 64 bit kernel above and beyond the most basic (>3 - 4 GB) question. I've seen first hand when working with large files in Photoshop on 4GB Macbook Pro, it benefited greatly from booting into 64 bit mode. Files that large must still be mapped into memory when editing, just as any large file manipulations could potentially bump you into that space. Here's a good list from Wikipedia:
* Some operating systems reserve portions of process address space for OS use, effectively reducing the total address space available for mapping memory for user programs. For instance, Windows XP DLLs and other user mode OS components are mapped into each process's address space, leaving only 2 to 3 GB (depending on the settings) address space available. This limit is currently much higher on 64-bit operating systems and does not realistically restrict memory usage.
* Memory-mapped files are becoming more difficult to implement in 32-bit architectures, especially due to the introduction of relatively cheap recordable DVD technology. A 4 GB file is no longer uncommon, and such large files cannot be memory mapped easily to 32-bit architectures; only a region of the file can be mapped into the address space, and to access such a file by memory mapping, those regions will have to be mapped into and out of the address space as needed. This is a problem, as memory mapping remains one of the most efficient disk-to-memory methods, when properly implemented by the OS.
* Some programs such as data encryption software can benefit greatly from 64-bit registers (if the software is 64-bit compiled) and effectively execute 3 to 5 times faster on 64-bit than on 32-bit.
* Some complex numerical analysis algorithms are limited in their precision by the errors that can creep in because not all floating point numbers can be accurately represented with a small number of bits. Creeping inaccuracies can lead to incorrect results, often leading to attempts to divide by zero, or to not identify two quantities as being identical for practical purposes. International Computers Limited added 128-bit support to the ICL 2900 Series in 1974 largely as a result of requests from the scientific community.
It is odd that Apple hasn't enabled a 64 bit EFI for 64 bit capable systems. As long as the drivers existed for the basic system hardware, the 'option' to do so should at least be there. I can't imagine that 64 bit drivers don't exist for typical hardware, even if it's a few years old.
The transition from 32 to 64 bit has taken about 20 years before people got serious about making the full switch on a desktop. 32 Bit 8088's hit the market around 1980. Considering 64 bit processors for the desktop didn't really hit until, about 1995-1997 or so. It's taken another 10 years before the OS's have started catching on. About 25 years total between architectures from first production to general adoption on the desktop.
You should still have plenty of use out of your old Mac if the industry takes about the same amount of time. I'd guess about 2020 before 32 bit OS support is just about gone. Apple tends to hit the curve early, so maybe a bit earlier for them, but you should have many years left before you have to make that decision. The industry moves kinda slow and people move even slower when it comes to general adoption