[objclxt]

I'm prepared to give Microsoft the benefit of the doubt here, and suggest that Office is a bit more complex than your average user-land application. I suspect a lot of the code is either quite old or low-level, to a much larger degree than a typical app. It's not just Microsoft - think about how long it took Apple to migrate iTunes from Carbon to Cocoa, or Adobe to get 64 bit PhotoShop on the Mac.

[stephencanon]

The limiting factor in both Carbon -> Cocoa and 64-bit Photoshop was porting to a completely different API layer, which turns out to be vastly more invasive than changing architectures. Even for very complex userland programs, changing architectures typically doesn't require changes to more than a tiny fraction of the codebase (unless one is porting to something truly exotic, but ARM and x86 are really quite similar from that perspective). You end up spending a few months chasing down bizarre bugs, but the actual scope of the changes is always fairly small.

[MBCook]

I would agree that Office is probably a beast to port due to its long history and large code base, but that still doest explain why it should be considered an achievement for Office to run at all on ARM. ARMs are in the same ballpark as x86, clock for clock. It's not like its a 50x performance difference.

Mythbuster's argument just isn't making sense to me.

[Mythbusters]

It's not the difference in performance but having to compile against a different architecture altogether. These two are architecturally different and porting an old legacy app like office cross platform must not be an easy feat. I don't see examples of old apps easily being ported over across platforms.