But you may be wondering: “I thought the iPad and iPhone 4 had an A4 processor, not a Cortex A8?!” The A4 is in fact the whole applications System on a Chip, which includes not only a Cortex A8 core, but also graphics hardware, as well as video and audio codec accelerators and other digital blocks. The SoC and the processor core on it are very different things; the processor core does not even take the majority of the space on the silicon die.
ARMv7 support on the latest devices would be pretty useless if you couldn’t take advantage of it, so you can do so, but always doing so would prevent your code from running on earlier devices, which may not be what you want. So how do you detect which architecture version a device supports so that you can take advantage of ARMv7 features if and only if they are present? The thing is, you don’t. Instead, your code is compiled twice, once targeting ARMv6, and once targeting ARMv7; the two executables are then put together in a fat binary, and at runtime the device will itself choose the best half it can support. Yes, Mach-O fat binaries are not just for grouping completely different CPU architectures (e.g. PowerPC and Intel, making a Universal Binary), or 32 and 64 bit versions of an architecture, but also two variants (cpu subtypes, in Mach-O parlance) of the same architecture. The outcome is that from the viewpoint of the programmer, everything gets decided at compile time: the code compiled targeting ARMv6 will only ever run on ARMv6 devices, and the code compiled targeting ARMv7 will only ever run on ARMv7 (or better).