Its good to bring this up. I had my suspicions that FPGA was doing some sort of emulation. As I could not see any other way for a chip with a certain architecture to replicate exactly 2 or more hardwares.
But I guess it is still good to have some possible alternatives to play games for enthusiasts
The clue is in the name.
Field Programmable Gate Array, that is to say it is a selection (array) of gates aka transistors (computer chips are but large piles of transistors --
https://www.instructables.com/id/Logic-Gates-with-NPN-transistors/ ,
https://www.electronics-tutorials.ws/combination/comb_7.html , and everything is adding when you get down to it -- adding is adding, subtraction is adding, multiplication is long winded adding, division is adding if you do logarithms, and basic logic gates will tell you how to compare inputs to see if they match/are 0/are some number/are less than some number...), you can arrange (program if you will) out in the field rather than having to play with all the fun chemicals, clean rooms and a billion dollar factory. They are expensive as you like and quite power hungry for the performance they muster (though modern stuff is still reasonable enough for use in a portable device with still enough grunt to replicate these decades old chips)
With a good enough knowledge of either the transistors in question
Or the manuals for the chips (they specify what instructions are there, and how many cycles they are supposed to take, any decent programmer/emulator manual made after the fact will also mention what goes for stuff outside what the chip originally did) you can replicate this.
Do this right and
Do it half arsed and you have the same problems you get with normal emulators where timing might be messed up, features might not be implemented and code that relied on either will not be happy (see also the video above)
https://arstechnica.com/gaming/2011...-3ghz-quest-to-build-a-perfect-snes-emulator/
https://trixter.oldskool.org/2015/04/07/8088-mph-we-break-all-your-emulators/
FPGAs are wonderful things and a serious avenue for future use, especially in the clone console and tricky to emulate devices field (emulating one chip is trivial, emulating 15 fairly fast ones all at the same time and keeping it all in sync and operating in real time is a far harder task), and what they can do will take all the power of a modern desktop and more if you want it to, however you do eventually hit a diminishing returns limit where the vast majority of games will appear as they did on the original device, if not better as emulation being just code also means unfettered access to memory (easy cheats, savestates, debugging), scope to scale images or even do fun things like widescreen, scope to broaden input emulation, scope to speed things up... such things are also within reason for a FPGA (you are literally defining things, no great shake to put in a means to copy memory, tweak it, redirect things, ignore security, expand upon the hardware's scope and whatever else) but you are then tasked with balancing those abilities and emulation accuracy where software emulators have fewer concerns.
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