But what if the Arduino Uno was released in 1980 ... No USB-UART (which also means no USB programming), a different pin layout (Arduino shields likely won’t fit) and more I/Os than the ATmegas ...

The Uno also has a limited number of pins, making it difficult to work with when the project requires plenty of input and output components. However, these two areas are where the Arduino Mega shines.

This board also features 128 MB of RAM, 8MB of Flash and the usual compliment of Arduino pins in a Leonardo-compatible layout. Also on the SoC is a PCIE bus, Ethernet, a USB 2.0 host, and an SD card.