It didn't use cards, but paper tape (as seen in the BBC clip). So I guess, in theory, it could have gone on forever if you just glued a fresh tape to the end of the old one.
>"It was, of course, slow, not much faster than hand calculation on single operations, but fully automatic, extremely reliable and utterly relentless. It took little power and could be left unattended for long periods; I think the record was over one Christmas-New Year holiday when it was all by itself, with miles of input data on punched tape to keep it happy, for at least ten days and was still ticking away when we came back."
>"It was, of course, slow, not much faster than hand calculation on single operations, but fully automatic, extremely reliable and utterly relentless. It took little power and could be left unattended for long periods; I think the record was over one Christmas-New Year holiday when it was all by itself, with miles of input data on punched tape to keep it happy, for at least ten days and was still ticking away when we came back."
http://www.chilton-computing.org.uk/acl/literature/reports/p...