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

The new announced revision of the iconic UNO board, which will expand the concept of the open-source brand’s most iconic and popular product The Arduino UNO R4 preserves the well-known features of the ...

Yes, I have just joined the countless hundreds who have started are currently using the “Arduino” platform for learning. I have to say it is the EASIEST microcontroller to use that I have come across.

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.