I've actually been looking to explore this for literally ages... I hope to play with this sort of thing someday at both ends of the spectrum, to get a bit of a

I've actually been looking to explore this for literally ages... I hope to play with this sort of thing someday at both ends of the spectrum, to get a bit of a practical education on how architectures have developed over the past two dozen years or so, and hopefully to have a bit of fun. On the one hand, I'm really, really interested to understand how the pieces fit together such that it was possible to have supersmooth sidescrolling on the 4MHz CPU in a Game Boy. On the other hand, I want to learn how to best optimize for the CPU/GPU targets in current- and next-gen desktop and portable devices (PCs, laptops, phones, tablets, etc). It might sound bizarre to want to get the most out of even a 4k-core GPU just for 2D (with maybe some fancy parallax), but 3x4K is going to be a thing more frequently than not going forward... and a pixel-perfect 144fps sidescroller would look truly amazing on something like that. I want to understand both sides of the coin in-depth so I can optimize for each but also maintain a sense of balance: the majority of game engines are overwhelmingly future-oriented, and when presented with older hardware something like Unity will invariably choke or at least stutter, and Box2D likely would as well. I do at least realize the complexity in building a game engine from the ground up - like I said before, this is purely for fun and education - but I have no idea where to actually start, no knowledge of older architectures (and their quirks), I still need to learn assembly language (!!) and machine code (it's on the todo list... has been for months...), etc etc. Advice will truly be hugely appreciated.