[uxhacker]

Originally the PNR when the reservation systems where built in the 1960’s and 70’s the six / seven / eight digit reference was the hash of the physical location in memory of the booking. It would take very few cpu cycles to recall the booking.

Nowadays of course the booking reference is virtual.

[hirsin]

Should I read this as a reversible hash? I can't imagine it works this way, have you got any pointers to learn more about early sabre ?

[uxhacker]

You can read here https://www.jstor.org/stable/249202?read-now=1#page_scan_tab... I am sure there are other resources available.