How does PPSSPP work?

[TheDax]

The PSP has its own OS with its own kernel, and the games just run on top of the kernel in user mode. The games don't really care about if the kernel is really there or not, so long as the functionality they need is provided, so this allows us to provide an HLE (high level emulation, meaning there's little need to emulate a lot of things, or even the real operating system) implementation of Sony's OS. It provides a good speed benefit too, since every time a game asks for something from our "kernel", it switches to native ARM or x86 code instead of having to be emulated MIPs code. This comes at a cost, though. We don't know exactly everything about every kernel function, so some games might crash if functionality is missing, takes too long, doesn't take long enough, etc.

I think that pretty much covers everything, but if I missed anything, Henrik and/or Unknown might chime in.