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.

Some other solutions for extra IO would be to buy an Arduino Mega with 54 digital IO pins or the Muxshield which gives you 48 IO (and is stackable for other shields). An advantage of using the two ...

[Andy] didn’t want to use up 24 pins on his Arduino, so he used a latch to multiplex the lowest 8 address lines and the data lines together. With the 512KB RAM expansion installed, the Mega is ...