It was preceded by the more advanced Burroughs B5000, which had a stack-based architecture, was directly programmable in Algol60, and had virtual memory.
You beat me to it. I counter that "first" part every time I see it because it was both second and an inferior machine. To think they spent $5 billion on it. I still don't have a number on what B5000 cost to develop. That would be interesting comparison.
EDIT: $500mil-$1bil on development part per another comment.
The difference is that the B5000 was a single machine while S/360 was a platform of compatible machines with a wide range of prices. IBM also maintained backwards compatibility while it appears that the B6500 did not.
Not to nit-pick but it was Burrough's Algol systems programming dialect rather than straight Algol60. Damned impressive, yep. (See Alan Kay's various talks about computer history.)
