The Boss RC-20 and RC-20XL are both loop station pedals, but the RC-20 features limited memory with a maximum of 5 minutes of recording time and a simpler interface. In contrast, the RC-20XL offers expanded memory, allowing for up to 16 minutes of recording time, and includes additional features such as multiple undo/redo functions and the ability to store and recall loops. The XL model also has a larger display for better visibility and enhanced user control. Overall, the RC-20XL provides more versatility and functionality for looping performances.