è iPhone 5S 2 volte più veloce di iPhone 5 in Graphics Task (come Gaming) a causa della CPU a 64 bit?

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Phil Schiller ha parlato di " iPhone 5S "

This is the first-ever 64-bit processor in a phone of any kind. I don’t think the other guys are even talking about it yet. Why go through all this? The benefits are huge. The A7 is up to twice as fast as the previous-generation system at CPU tasks, and up to twice as fast at graphics tasks, too.

-Phil Schiller, keynote di Apple al 4  Infinite Loop il 10 settembre 2013 (fonte: Wikipedia)

Poiché la memoria è solo 1 GB per "iPhone 5S", quindi In che modo la CPU a 64 bit è più veloce della CPU a 32 bit?

Ho sentito che, nell'ambiente desktop, per ultilizzare l'architettura a 64 bit abbiamo bisogno di più di 4 GB di memoria.

Molto confuso?

    
posta Tim 28.05.2014 - 13:29
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1 risposta

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Questo copre praticamente tutto ciò che è necessario sapere sui vantaggi del passaggio da Apple ad ARM64.

link

tl; dr conclusione / risposta dal link

It's also important to point out the things that "64-bit" does not refer to, as there's a lot of confusion in this area as well. In particular, "64-bit" does not include:

  1. Physical RAM address size. The number of bits used to actually talk to RAM (and therefore the amount of RAM the hardware can support) is decoupled from the question of CPU bitness. ARM CPUs have ranged from 26 bits to 40 bits, and this can be changed independently from the rest.
  2. Data bus size. The amount of data fetched from RAM or cache is likewise decoupled. Individual CPU instructions may request a certain amount of data, but the amount of data actually fetched can be independent, either by splitting the fetch into smaller parts, or fetching more than is necessary. The iPhone 5 already fetches data from memory in 64-bit chunks, and chunk sizes of up to 192 bits exist in the PC world.
  3. Anything related to floating-point. FPU register size and internal design is independent, and ARM CPUs have had 64-bit FPU registers since well before ARM64.

"64-bit" A7 is not just a marketing gimmic, but neither is it an amazing breakthrough that enables a new class of applications. The truth, as happens often, lies in between.

The simple fact of moving to 64-bit does little. It makes for slightly faster computations in some cases, somewhat higher memory usage for most programs, and makes certain programming techniques more viable. Overall, it's not hugely significant.

The ARM architecture changed a bunch of other things in its transition to 64-bit. An increased number of registers and a revised, streamlined instruction set make for a nice performance gain over 32-bit ARM.

Apple took advantage of the transition to make some changes of their own. The biggest change is an inline retain count, which eliminates the need to perform a costly hash table lookup for retain and release operations in the common case. Since those operations are so common in most Objective-C code, this is a big win. Per-object resource cleanup flags make object deallocation quite a bit faster in certain cases. All in all, the cost of creating and destroying an object is roughly cut in half. Tagged pointers also make for a nice performance win as well as reduced memory use.

tl; dr tl; dr

  • RAM (memoria) è disaccoppiata dalla CPU bitness e non ha gioco nella sua performance
  • 64-bit non da solo 2 boost
  • A causa della transizione verso Apple a 64 bit, è stato introdotto un modo intelligente per migliorare le prestazioni
risposta data 28.05.2014 - 13:37
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