1. Cell phones may cross over the 2 GB boundary soon,
but ARM can already comfortably address terabytes
of RAM through segments, as mbell notes. At worst,
we're limiting individual applications to under
2 GB of RAM--not the end of the world.
2. While being able to address 64 bits at once is useful
for some computing tasks, *most* of those (scientific
computing being a biggie, but also some parts of video
editing or sound mixing) just aren't ones people
currently do on a cell phone. They likely will
eventually, but the hold-up there is as much about
getting the data onto the phone in the first place as
actually doing anything significant with it.
3. Adding 64-bit wide paths adds a *lot* of silicon for
something that would currently not get used at all,
and in the future won't get used much for quite some
time. More silicon means a shorter battery life and
more heat--not exactly what you want in a cell phone.
Look at how much effort ARM's going to in big.LITTLE
just to let them go superscalar, let alone 64-bit.
4. Finally, the on case where you might get good
benefit--games--are better served through GPUs and
ARM's existing NEON instructions, which already work
on I believe 128-bit-wide values.
So those are all the reasons why I don't see the lack of 64-bit ARMs right now as a real problem. And, indeed, if ARM were only getting used in cell phones, I wouldn't honestly see a pressing need to go to 64-bit chips, period.But ARM wants to move into servers, and there, the situation's obviously very different. 64-bits is a no-brainer for any moderately sized database, and that's where I suspect ARM really needs this ISA. But those will take a few years to build and gain acceptance, anyway; they've got time.