Originally posted by Messiah
So can you do all of these things with a 32bit OS on a 64bit CPU, or do you need a 64bit OS as well?
Depends on what "is" is. Er, wait.
Minimal changes should make Mac OS X "64-bit-sane" (making up a term) so that it can run on 64-bit hardware. A different (I think, but still small) set of changes will allow access to 64 memory accesses for programs deliberately written to do 64-bit things. Let's call that "64-bit aware"
Both of those _could_ be a x.x.1 upgrade, and are (almost) typical of Apple always having slight changes in system software for new hardware.
BUT: This would _not_ be the "full 64-bit OS". To do _that_ will require more work on the provided libraries etc. Like having the Quicktime team pour over Quicktime looking for any function that could be written to have both a 32-bit version and a 64-bit version.
So iCal just needs "64-bit sane" to go 2x as fast.
Photoshop will go 2x at "64-bit sane"...
...but be able to access more memory/plugings at "64-bit aware"
Oracle will see a tremendous boost (Greater than 2x) at "aware"
But for all the nitty-gritty things that might see a _little_ improvement, that's going to wait for Apple to put out the "full 64-bit OS".
So what I'm trying to say is the 64-bit sane, or 64-bit aware tweaks, which aren't earth-shattering changes -> 90+% of the benefits. But even at this point the OS hasn't necessarily been tweaked _itself_ to improve its speed. Just to provide access to the hardware for the people that _need_ access.
So when you say" because if you're running a 32bit OS, it won't reveal the 64bit capabilities of the CPU to the applications?" You are right... and wrong.
The central bits have to be altered to understand & provide access. aka make it 'sane' and 'aware'. This isn't a 2-year undertaking.
But at that point the OS itself might not be able to (say) handle 4 billion items in a single finder view. -> All the frameworks/libraries/included programs do NOT need to be fully 64-bit, which _would_ be a major undertaking.
Edit: Heh, and Programmer contradicts me
I think he'd call a '64-bit aware OS', one that provides access without necessarily having a full rewrite a '64-bit OS' though.
So a "mostly 32-bit OS" that understands 64-bit, and exposes the 64-bit hardware/allows apps access -> _most_ of the benefit.
You aren't being obtuse, this is confusing, and I still don't think I explained it well... but I have to run for now.