Checking system-wide uptime on several Cisco hardware platforms

We all know adding redundant supervisors/CPUs to any given system, we can increase the uptime for that system. With In-Service Software Upgrade (ISSU), Cisco hardware even allow us to upgrade the operating system software on-the-fly without stopping the whole system.

Flowers of Cassia fistula was blooming together in southern Taiwan starting from mid-May.
This photo was taken around this location in Baihe District of Tainan City, Taiwan.

An interesting question might be asked. Does Cisco hardware keep track of system uptime even upon supervisor/CPU failover events? And how to display the system uptime, in addition to individual supervisor/CPU uptime?

I spent some time and I summarize my findings in this post.