Απο οτι διαβάζω, και χωρις τα 4gb, υπαρχουν σημαντικα πλεονεκτηματα με τα 64bit:
But chip experts say that there are plenty of gains to had even from a 64-bit chip without 4GB of addressable memory.
For one thing, 64 bit integer math will allow the A7 to execute operations much faster than the 32-bit A6. “The fact that the A7 has twice as many processor registers means that more operations can occur without the processor using main memory, which is slower to access,” Carl Howe, VP of research and data sciences at the Yankee Group told AllThingsD. “This means for that, for some codes, the A7 will be twice as fast (or faster, depending on how many memory accesses the original code had) to run code, because the processor doesn’t have to use main memory as much.”
This should also improve battery life, as well.
Another benefit: ARMv8, the architecture on which the A7 is likely based, has a very efficient instruction set that’s great for resource-intensive applications. As Kevin Krewell, senior analyst at the Linley Group and a senior editor of Microprocessor Report, told AllThingsD, “The ARMv8 instruction set is clean-slate approach with many improvements. Even without 4GB of RAM, the A7 should make it easier to build larger applications like PC-class games and programs. Apps can now become real desktop-class programs and games.”
The caveat here is that Apple must maintain backwards compatibility with legacy 32-bit apps until the 64-bit ecosystem really kicks in. Said Krewell, “The vast majority of programs will still use the 32-bit mode, so the benefits may be slow to come.”
Finally, with the 64-bit A7, Apple has made it possible for developers to take the 64-bit apps they’re written for the Mac and bring them to iOS 7 with relative ease. And that is a huge benefit, indeed.
“Because Apple makes the development environment and has updated those tools for 64-bit architectures, a developer only really needs to recompile their application to make it 64-bit compatible — assuming they haven’t done anything non-standard with their code,” said Howe. “This will not be true with Android, by the way. The Android Java app and native app environment will need support from Oracle, who owns the Java environment as well as 64-bit support from the Android kernel. Android has a lot more moving pieces to coordinate, and will take longer to go to 64-bit.”
So, while this early transition to 64-bit is most certainly a long-term play for Apple, it’s not without some immediate and important short-term benefits — even without more than 4GB of memory.
http://allthingsd.com/20130913/apples-iphone-5s-the-a7-chip-and-that-64-bit-question/