The mainline boards feature an ARM Cortex processor. Although not quite ... Things aren’t quite so simple on the Arduino side of things. The Arduino Uno I’ve used as a reference has 32-pin ...

The Arduino Nano and Uno are equipped with very similar processors (the chip that essentially serves as the brain of the board). The Nano features an ATmega328, while the Uno sports an ATmega328P.

[Damian Peckett] has implemented an Apple ][, its 6502 processor, and a cassette port, all on an Arduino Uno. If that wasn’t enough, he also uses a PS/2 keyboard for input and outputs analog VGA.