This is probably very easy to answer but I am still trying to wrap my mind around ARM vs Intel type processors. I understand that you cannot run Windows 8 or Microsoft Word on the Pi because it is an ARM processor. Does Android run on ARM and if so does that mean all apps on Google play would work with the Raspberry Pi(not considering the load on the GUI)? How can you know if something will run on an ARM processor?
ARM is actually a family of processor instruction sets. The A/B/+ model pis have a processor which is ARMv6, whereas the Pi 2 is ARMv7. A few things to note about that:
- ARMv7 is backward compatible with ARMv6, meaning an ARMv7 processor can run code compiled for ARMv6. However, the inverse is not true: an ARMv6 processor cannot run ARMv7 code.
- Most (but not all) Android devices are ARMv7 based; I don't know if there are any that are ARMv6.
To run an Android app, you need an Android userland; you cannot run them on a GNU/Linux system except with the use of an emulator. Even if you could get this to work on a pi, it is going to be too slow to be worthwhile. It is noticeably slow on an a big x86_64 desktop; the emulator is intended for development purposes.
You could install an Android userland on a pi. Since there are few if any ARMv6 Android devices, finding such a userland will not be easy. It is open source and can be compiled however, and people apparently have done this (see here halfway down), although it sounds like it is a pretty old version (2.3) -- but of course that article is two years old.
Android on the Pi 2 is much more feasible; besides the architecture, a big issue with Android is fitting it usefully within 512 MB of RAM. 1 GB, though, is enough. I'd assume sooner or later this will happen.1
Razdroid is project which aims to port Android 4.0 to the pi, although it does not appear to be ready for prime time.
1. Perhaps the reason more effort hasn't been made here is because there are already a number of ARMv7 dev boards in the Pi 2's niche that do have official Android images available.
The processor is not really the problem. The reason Windows software does not generally work on ARM is because it is closed source and Microsoft have not released ARM versions.
Although Android has its roots in Linux the kernel is incompatible with the Linux kernel used on the Pi.
If you can find a way of running Android on the Pi you will be able to use Android apps. No one has been able to find a satisfactory way to run Android on the Pi.
You find out if software will run on a platform by seeing if there is a version available for the operating system you want to use on a platform. The pre-requisite is that the operating system itself will run on the platform.