[jamestnz]

According to the release notes for Safari 9 [1], it's because of performance concerns: "Apps containing content blocking extensions for Safari on iOS are available only on 64-bit devices, due to performance limitations of 32-bit devices"

I imagine there's no real reason that content blocking shouldn't work on 32-bit devices, but that Apple are trying to hit certain minimum performance numbers (for marketing/brand purposes)... and I'm sure they won't be upset if this should happen to encourage a few users of older devices to upgrade (i.e. forced obsolescence).

I think there are various examples of Apple doing this kind of thing (saying a certain generation of hardware is supported by software X, but then you find various things are disabled for you). Not exactly the same, but pre-2011 Macs cannot mirror their display via AirPlay (Apple saying the video hardware isn't up to the task) -- at least not until you install the third-party app AirParrot, then it works fine.

[1] https://developer.apple.com/library/prerelease/ios/releaseno...

[ytch]

Maybe 32/64 bit isn't the issue, Apple just choose it as a flag to exclude slow CPU?

[choppaface]

The 64-bit CPUs have a wider (and thus effectively faster) bus, and content blocking is probably rather strenuous on CPU cache (lots of string/pattern matching?). While the 64-bit cutoff is likely mostly a marketing artifact, content blocking on 32-bit CPUs could actually be 2x slower or worse than 64-bit CPUs and thus make page rendering times very painful for some sites.

[Yetanfou]

Nope, it is pure marketing. There is no technical reason whatsoever for ad-blocking to require a 64 bit CPU or databus. It actually works fine on a single-core sub-Ghz ARM7 like that used in my phone (Motorola Defy) with all of 512MiB of memory.

[choppaface]

Huh, did you really run iOS9 ad blocking on a Motorola Defy? I definitely believe Apple's position is 99% marketing, but I can imagine there are some common pages that load really slow on older hardware. I've seen older iPads crash consistently trying to render complicated pages.

[Yetanfou]

Of course I did not run iOS on that Defy, why would I? Ad blocking was everywhere before apple finally decided to allow it on iOS. Inside those idevices are ARM-based CPUs, just like the ones in most other mobile hardware. What difference does it make whether the OS is based on Linux (Android), Mach/BSD (iOS) or even Windows (...Windows)? A regexp is a regexp after all...

The Defy does not crash rendering complex pages. It can get pretty slow though, reason for running extensions like NoScript for Android [1] (which runs just fine on the Fdroid.org Fennec build, ie. Firefox without the nasty bits) and uBlock origin.

[1] https://noscript.net/nsa/