The Arduino Uno-compatible board has an MCS-51 (often called 8051 instead) instead of the usual ATmega328P/ATmega168. Specifically, [ElectroBoy] uses the AT89S52 .

Both the Arduino Nano and Uno can be powered via their integrated USB connectors. This automatically supplies regulated 5V power to the board, allowing you to use any USB-supported power source ...

Arduino, the world's leading ... Arduino Uno - The World's Most ... R3 and 32-bit UNO R4, significant efforts are being made to ensure maximum backward compatibility with existing code examples ...