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Comment by microtonal | Hacker News Reader

I don't see the huge benefit yet of using a 64-bit CPU in a phone. Sure, it may be useful computations on 64-bit numbers and I assume that it'll have more registers. But if pointers are also 64-bit, it's a bit of a waste of memory.

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Memory and '64bit math' aren't really the drivers here, 64bit archs generally have a lot more registers and allow better packing of SIMD instructions. Both can give large performance increases, particularly the later when a lot of what you plan to use that power for are things like image manipulation.

More broadly this is probably a move from ARMv7 to ARMv8, which brings about a bunch of performance improvements besides 64-bit-ness: more registers, double-precision floating-point SIMD, hardware AES and SHA extensions, etc. This probably mostly opens up performance improvement potential for games, but things like SSL could also get faster.

A 64-bit virtual address space also makes for much more effective address space layout randomization.

I imagine it also helps them deal with doing the h264 encoding and such that they need to get the lightning connector to do the hdmi output that they built. The added SIMD stuff in ARMv8 was also largely targeting video encoding also I believe.

Twice the integer and floating point registers, IIRC. Their benchmarks were placing it as twice as fast as the previous gen.

It'll also enable tagged pointers, which will probably speed up Objective-C code and encourage people to move away from using primitives types.

PL implementors tend to not agree:

(RubyMotion creator, follow the thread:) https://twitter.com/lrz/status/377486518719623168

Pointers nowadays are not just used for addressing things.

What's PL?

Programming Language. It's a bit odd, because they mostly implement runtimes, but PL stuck :).

Programming language.

It allows more than 4GB of RAM in the future, I suppose. I'm more surprised to see them advertise it. I thought Apple was above specs?

Seems a bit crazy now for a phone, today, but the new consoles have 8GB and the iPhone is vastly more powerful than the original Xbox. The 5S is probably on par with the 360 now.

Shifting to 64-bit makes a lot of sense for future-proofing.

Sure, but not on this phone.

That's why I put the yet in between. I don't expect that the 5S has more than 4GB RAM.

Of course, it is possible to address more than 4GB in a 32-bit operating system with processor extensions, if you limit the address space of processes to 4GB (see e.g. PAE). I don't expect that we'll see many applications needing more than that soon. Maybe games?

Address space isn't just about ram. Memory mapped files are used extensively in iOS, 64 bit means basically no limits on memory mapping size from file in flash.

I know. I still don't believe that iPhone Apps have such requirements in the near future. Except for possibly games. But currently it would not be very attractive for studios to target the 5S only. So, I assume that your sibling is right, it is more of a preparation for the future (apart from the benefits of a new ARM version).

The one thing they kept emphasizing was that the A7 was forward-looking. Presumably meaning, they have a roadmap for what they're going to do with it.

Historically, Apple is only above specs when the specs they're talking about are inferior to the rest of the market. When they've got something better, there's no end to the bragging.

I don't see the huge benefit yet of using a 64-bit CPU in a phone.

...unless the phone becomes more and more of a gaming platform.

On a 4" screen?

Airplay mirroring.

ARM chips aren't that register starved, however, the 64 bit ARM chips now have 31 registers instead of 16.

It'll probably cause some new headaches for developers having to compile two versions.

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