Apple Announces A7, World's First 64-bit Smartphone SoC

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• Azurael - Wednesday, September 11, 2013 - link

  Are the people who are implying 64-bit implies an automatic performance increase talking about x86? x86-64 is a weird case because you get twice the registers in long mode on an AMD64 CPU, which increases performance. That's not the case with other architectures, in fact outside of certain very specific usage cases (big scary scientific data processing) and the need to address more RAM - the performance difference is nil, or even worse a decrease due to shuffling about twice as much data... I can vouch for 32-bit userland being faster on the whole on UltraSPARC and PPC64 - I don't see why that wouldn't be the case on ARM unless there's something I don't know about the architecture.
  
  But Apple have always been big on the marketing - they know 64-bit is useless on mobile... Of course the new architecture is very interesting for different reasons others have outlined here, but '64 bit' sounds impressive when you're faintly aware that previous mobile phones had 'less bits', no? Just like it did when Nintendo were marketing the N64....

• Kevin G - Wednesday, September 11, 2013 - link

  The amusing thing here is that you're giving a case for 64 bit to be slower. Look at how the numbers are fully represented:
  
  0x00000000000000000000000000000001
  
  Vs
  
  0x0000000000000000000000000000000000000000000000000000000000000001
  
  For data paths of equal length, the 32 bit chip would be able to move more packets of data even though the throughput in raw GB/s would be the same.
  
  Purely going to 64 bit has two main advantages: more addressable memory and fast 64 bit integer computation. When ARM and x86have gone 64 bit the architecture changed more than the size of the general purpose registers.

• kbk0000 - Wednesday, September 11, 2013 - link

  You could argue doubling of registers has nothing to do with 64 bit, had someone was building this processor from ground-up, but that's not the case here. ARM v8 ISA doubles the number of registers, and ARM v8 is 64 bit ISA, so doubling up registers would have been not possible without moving to 64 bit. Plus, there are other improvements ARM made to v8 over v7, so this argument of 64 bit "just preparing for larger memory" is really a huge overgeneralization, because the implementation of ARM v8 architecture, not just 64 bit, should provide performance improvement in many areas, just like how ARM's own A57 design generally performs better all around than A15 (they have similar pipeline, but A57 is v8 architecture whereas A15 is v7).

• raptorious - Tuesday, September 10, 2013 - link

  Your logic would be correct if a 64-bit ISA were the only way to execute instructions on 64-bit or larger data types, but that is not at all the case with the ARM v7/v8 ISA's. With Neon and VFPv4 extensions, the ARMv7 (32-bit ISA) is very capable of doing 64-bit data operations (http://infocenter.arm.com/help/index.jsp?topic=/co... Sure, 64-bit ISA's typically give you 64-bit general purpose registers (and 32-bit ISA's typically limit you to 32-bit general purpose registers), but those aren't the primary determinant of performance in throughput dominated workloads (implied by your comment about "available resources / performance of the pipeline"). FP/NEON registers are the limiting factor in this case, and ARM v7 (a 32-bit ISA) supports up to 64-bit registers in that domain.

• Daniel Egger - Tuesday, September 10, 2013 - link

  But NEON always operates on 128bit. It's not efficient to do single 64bit operations using NEON at all.

• Hamranhansenhansen - Tuesday, September 17, 2013 - link

  >> 64Bit isn't just for more addressable RAM.
  
  > What else is it for?
  
  Running 64-bit code.

• soryuuha - Tuesday, September 10, 2013 - link

  xinthius..please defend/elobrate your comment. I would love to hear more about what you've preached.

• xinthius - Thursday, September 12, 2013 - link

  Stated, not preached. I'm not religious, and nor is this a religion.
  
  64Bit can related to either the address bus, the data bus or a set of registers. Typically the old description of the Bit was the address bus, relating to how much memory a system could address. This is not the case anymore as 64Bit mainly relates to the size of the general purposes registers, not the amount of RAM that is addressable.

• DanNeely - Tuesday, September 10, 2013 - link

  I suspect it's mostly to maintain architecture parity with the upcoming iPad refresh. A 4GB phone this year would surprise me; a 4GB tablet would not.

• Krysto - Tuesday, September 10, 2013 - link

  Apple will not put 4 GB of RAM in iPad. They're usually behind the curve in amount of RAM.