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Comment by __bjoernd | Hacker News Reader

But then all software will have to be shipped as ARM and as x86 binaries. Sure, that is possible engineering-wise, but at least the binaries are going to double in size. And there may be slight issues when you migrate applications between the ARM and x86 world with respect to data layout etc.

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They already did that on the PPC -> x86 switch, and again on the 32bit to 64bit switch. iOS does it as well for the different version of arm. For most applications the code is smaller than the rest of the resources, so it's not really that big an issue.

http://en.wikipedia.org/wiki/Universal_binary

Running two ISAs at the same time is way more complicated than simply shipping two versions of the binary within the same file.

OSX always did that, more or less. It seems like it's only in the last few months with Chrome switching to 64bit that it's been possible to stay 64bit clean. Same with iOS, even the 64bit arm devices have to keep 32bit armv6/7 versions of all the frameworks around to be able to launch older appstore apps.

Sometimes they slip up, and I think it was Skype that ran into problems where some releases of OSX shipped a faulty or missing 32bit driver for some particular iSight/FacetimeCam models.

(on the other hand, as you say, it might be more difficult to run a multi processor setup sharing RAM and buses across completely incompatible ISAs.)

Didn't Apple do something like that before?

You know, Universal binaries that contained both PowerPC and Intel within a single fat binary...

Double size binaries is nothing compared to the amount of storage you have today.

They did and still do, sometimes even 3 or more archs in the same binary;

On OSX: combinations of PPC, x86, x86_64 could be built

On iOS: default at the moment is a triple of armv7, armv7s, arm64, I believe. For a while used to be armv6+armv7.

Support for this dates all the way back to NEXTSTEP which ran on multiple architectures (68K, x86, and IIRC Sparc and/or PA-RISC) back in the 1990s.

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