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"The "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

"The "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." [1] https://www.mikeash.com/pyblog/friday-qa-2013-09-27-arm64-and-you.html https://www.mikeash.com/pyblog/friday-qa-2013-09-27-arm64-an...

makomk 13y ago
So basically, it's only really a substantial performance win because of a quirk of how Apple's 32-bit code was written, a quirk that doesn't apply to competing platforms.
- chaostheory 13y ago
  It will apply to competing platforms in about two years, when the first set of devices with 4 GB or more RAM start appearing.
- acdha 13y ago
  If you look at the history of desktop/server operating systems, it followed the same pattern as clearly explained in the article: problems start before 4GB and affect programming decisions as soon as users start working with files which aren't trivially small. Once 64-bit became the default, many small optimizations or larger design changes became easy enough that they actually happened and produced small but meaningful improvements
- wklauss 13y ago
  This specific case might only apply to Apple (I don't know, haven't read about it before) but the quirks of ARM's 32-bit instruction set surely apply to everyone else. The transition could have happen later, maybe, with not too much repercussion, but why not make the jump now, especially when you have a whole new OS engineered to take advantage of it?

makomk 13y ago

So basically, it's only really a substantial performance win because of a quirk of how Apple's 32-bit code was written, a quirk that doesn't apply to competing platforms.

chaostheory 13y ago
It will apply to competing platforms in about two years, when the first set of devices with 4 GB or more RAM start appearing.
acdha 13y ago
If you look at the history of desktop/server operating systems, it followed the same pattern as clearly explained in the article: problems start before 4GB and affect programming decisions as soon as users start working with files which aren't trivially small. Once 64-bit became the default, many small optimizations or larger design changes became easy enough that they actually happened and produced small but meaningful improvements
wklauss 13y ago
This specific case might only apply to Apple (I don't know, haven't read about it before) but the quirks of ARM's 32-bit instruction set surely apply to everyone else. The transition could have happen later, maybe, with not too much repercussion, but why not make the jump now, especially when you have a whole new OS engineered to take advantage of it?