The iOS simulator works at a higher level, simulating the operating system and its libraries, translating OS calls into OS X implementations and simulating events in the other direction like device rotation or low memory conditions. When you run an app on the iOS simulator, the app is compiled into x86 that runs natively on your Mac. Unlike the Android emulator, your iOS app won't run out of memory in the simulator because it's not constrained to any particular iOS device's memory limitations.