HASP was rebranded JES2 when 370 came along. IO devices were principally card readers and printers, but the neat trick was the internal reader.

Remember that JES2/3 were running batch jobs. TSO was shiny new.

OK, I need the joke explained. Is this a pun on SYNC?

No. The 50 was subject to intermittent failures (whether microcode or hardware I don't know).

SYNCH is how user mode exits are called from supervisor code.

COLT (Canadian On Line Teller) often ran (runs?) in supervisor state and in the bank I was working at the time would initialise a transaction buffer by setting it to all one's - very bad news when that buffer address was erroneously set to zero because some registers were not preserved across pseudo reentrant (a particularly repulsive term) interrupt points.

This invalidated all the New PSWs triggering an interrupt cascade such that the STOP key would not work because the instruction never completed. SYSTEM RESET (courtesy the IBM engineer) did the job.

The joke is about reliability. If you threw a computer that weighed a ton into the ocean it should sink 100% of the time.