Hesaid anecdata, but our company (that I recently joined) has been using AS/400 (now named IBM i, I believe) for 20 years and has had less than 6 hours of downtime.
As I understand it, one would definitely need training/study to interface with it.
These days, IBM i is specifically the operating system (so OS/400 successor), which is one of the operating systems (besides AIX and Linux) that run on IBM Power hardware.
As I understand it, one would definitely need training/study to interface with it.