Ran into a situation today where we had a mobile web app that was reported to be misbehaving on iOS 3.2. The Mac at work has the latest XCode and IOS 5 simulator loaded on it. So we thought it would be quite routine to just start a simulator running IOS 3.2 - after all this having simulators of different versions of the OS is pretty routine. Android makes it trivial and before that, Blackberry has always had different simulator versions for different versions of their OS. Truth be told, RIM probably overdid it. They had too many versions, a developer website that would drive even the most persistent BB fanboys to stark raving madness and documentation that took great pains to suck! Hell, its a separate rant altogether :).
Anyway, after clicking around Xcode for a bit, imagine our surprise when we found that only a device debugging package for iOS 3.2 was available as an updated package for Xcode. That didnt seem right - so off to Google and there’s a post on SE http://apple.stackexchange.com/questions/14128/how-do-i-install-the-3-0-iphone-simulator-on-xcode-4
Apparently, Apple doesn’t want you to test on previous versions (or atleast - 2 major versions before. Testing on last major version IOS4 is ok though). Now isn’t that absolutely ridiculous? Sure, Apple wants people to upgrade their phones to the latest OS versions and they’ve done a great job of ensuring that later versions of the OS work on older generation phones - but from a development tool standpoint, making tools to test your app unavailable is taking things too far. So tomorrow if my site/app doesnt work properly on a iOS 3 device, the user isnt going to blame Apple. Its the app developer who gets the bug report :(.
So once I’d made my peace with Apple’s decisions and diktats on what simulators I was allowed to play with, I reflected on it a bit. I think the key is that that IOS’s simulator is really just a simulator (ie software running on the host machine but mimicking a device). On the other hand, the Android emulator is actually a full qnx VM that’s totally isolated from the host machine. In IOS’s case, the simulator is sharing libraries and tools installed on the base OS - and as such, it would be quite hard to simulate older versions. In Android’s case, since each emulator is really like running a VM, you can have all the different versions at your beck and call. On the flip side of things, the emulator approach really slows things down - everything from booting up the VM to actually running code inside it whereas IOS simulator positively zips around. I’m not sure if this is indeed the case - it’s just my theory. Looking around on the net, I couldnt find a solid reference - so if you know of one, drop it in the comments.. I did find a few on SE/SO - but they were by no means conclusive http://stackoverflow.com/questions/4544588/difference-between-iphone-simulator-and-android-emulator