[Psyklax]

I have to say that I like Famiclones: I have one in the shape of a Mega Drive 2, labelled as Dendy (how the NES was known in Russia and other former Soviet countries) and it's a cheap and fun option for playing NES games through a CRT, without using a real NES (and the fact that you don't need to knock out the 10NES chip to play these wonderful multicarts is even better )

My question is: how do they work? I can read Wikipedia about NOAC stuff but it doesn't really explain it to me. I like emulation but I know it just can't beat the real thing. These Famiclones aren't emulation... but they're not exactly the real thing... what are they? How do they replicate what an original NES CPU and PPU do? And are there any flaws that would affect the playing accuracy? Other than little graphic and sound things that aren't really that big of a deal. I've noticed sometimes the audio on mine isn't quite perfect, like with Ninja Gaiden III (music sounds a little quiet). But what really matters is the playing, and I'm curious what's going on inside.

And you don't need to mention MMC4 and MMC5, Castlevania III, Disk System etc, I know it ain't gonna play them, but that's not a big deal, I can live without a few things (there's always emulation). So anyway, how exactly do these things replicate a real NES?

ps I'll take a Famiclone over a Retron 5 any day of the week. If I want emulation I can do it on an Android TV box, at least systems like the AVS have a point to them.

[Disch]

My question is: how do they work?

They're effectively hardware emulators.  Like the Retron-5, or the mapper support on the PowerPak or N8.  Someone just made new hardware that simulated the behavior of existing hardware.

And are there any flaws that would affect the playing accuracy? Other than little graphic and sound things that aren't really that big of a deal.

There are several... enough to where some emulators consider 'Dendy' a separate unit and can emulate it differently than PAL or NTSC.  Though the differences are mostly related to compatibility problems (MMC5, which you said you don't care about), and other minor timing quirks that could cause small graphics glitches (which you also said you don't care about).

Again, the Dendy is effectively an emulator in a box -- so it'll get close enough to play many games, but like any other emulator it'll never quite be 100% accurate.

ps I'll take a Famiclone over a Retron 5 any day of the week. If I want emulation I can do it on an Android TV box,

The Dendy is just as much an emulator as the Retron 5.  Only the Retron 5 is probably much more accurate.

[Jorpho]

Isn't the Reton-5 effectively a software emulator running on some sort of ARM hardware?  I'm thinking it's like the Atari Flashback, which used "custom" hardware in its early iterations, but then changed.
https://en.wikipedia.org/wiki/Atari_Flashback

I agree that such a solution probably ensures better accuracy than the alternative.

How do they replicate what an original NES CPU and PPU do?

In an exhausting and difficult process, someone reverse-engineered the hardware and made a custom integrated circuit (in a convenient and cheaply-replicated form) that behaves approximately the same way.

[Chronosplit]

Me and my wife note that Retron-5 cribs heavily from RetroArch, to the point that the libretro site made an article about it.

There are two types of Famiclones, all with similar accuracy: ones that emulate the software and ones that emulate the hardware.  The hardware side tends to have a slight edge, but sometimes it's just as even as software.