Seth Bling built a functioning Atari 2600 emulator in Minecraft. Not just the processor, or the box, but the whole thing, complete with cartridges and a television. The white flashing line you see in it is the television's scanning electron beam being emulated. You can watch dirt blocks turn to stone and back: that's the ones and zeroes in the Atari's memory. You can edit the memory, bit by bit, by punching it!
It takes Minecraft about three minutes to draw each frame, but Bling recorded a timelapse of it in action. Click through to the YouTube for a download of the Minecraft world housing the emulator. Here's a technical explanatory video:
I made an Atari 2600 emulator in vanilla Minecraft. It plays real Atari ROMs. Very. Very. Slowly. https://t.co/yDu9q8PVfb
— SethBling (@SethBling) December 6, 2016