As you are no doubt aware the new iPhone 5S and iPad Air have 64 bit A7 chips in them. And I can't understand why a smart phone would need a 64bit processor, but then only have 1GB of RAM. I mean the A7 chip is much faster, but not totally sure that is related to being 64 bit or just improved memory bus and better design. A7 has an L3 cache, and larger L1 cache which would make a big difference. And from what I have read the A7 is using duel channel 64bit memory bus, meaning it can move 128bits per cycle (but would this also work in a 32bit application, or just be the same as the A6). And having extra registers on the A7 may speed things up a bit. I can't see that there is much use for 64bit numbers in games yet, except maybe for doubles. But doubles are floating point numbers, which 32bit processors can easily work with at no extra overhead. So my feeling is that 64bit is really just so Apple can say we are first to have a 64bit chip.
There's a lot of FUD about this on tech blogs. Read this: http://www.mikeash.com/pyblog/friday-qa-2013-09-27-arm64-and-you.html The two big wins are improved Objective C performance and better handling of memory mapped files. The only real downside is increased memory pressure, which is a bit of a bummer since we're still stuck with 1GB devices.
Right now it won't be any use. Maybe in 1 to 2 years we will see it put to use. But it is good Apple have transitioned to 64-bit, as it is future proofing there chips. But yea, right now it is kind of dormant in the iPhone 5s & Air + Mini 2.
64bit architecture means speed and scalability This is a great news for gamers. It will allow to develop and port great 3d games and recourse hungry apps. Such engines like Unreal and Cryengine 3 will benefit from 64 bit. That means we'll see more big companies, more competition, better quality and lower prices.
Thanks for that article, it is really interesting. I didn't know they changed how the memory management is done. That would speed things, but it will only last while less than 64bits are used to reference memory.