The main characteristics of a single-board computer (SBC) are not only closely related to the performance of the processor and the size and speed of the memory, but also highly dependent on its connectivity and expansion options. And real time clock is an indispensable element in single board computer design.
https://www.perceptive-ic.com/news-detailed/An-Indispensable-Element-in-Single-Board-Computer-Design%3AReal-Time-Clock