I worked at a data center for a bank from 1997-2001. Processing ACH transactions for our data center involved a 1970s-era NCR mainframe, a decade-old MS-DOS PC

I worked at a data center for a bank from 1997-2001. Processing ACH transactions for our data center involved a 1970s-era NCR mainframe, a decade-old MS-DOS PC (they tried to upgrade it once, but the expansion card that handled the encryption wouldn't work with a faster system and a new card cost upwards of $10k), 9-track vacuum-fed tape drives, manually dialing a phone and then switching it over to a 9600 baud modem, and running batch-processing jobs which took greatly varying amounts of time to run. I did not handle the sending of ACH data back to the ACH system, only receiving it and processing it. I worked from 4PM "until it was done". Most nights this meant around 9:30PM. However, in situations like you described, where there is a bank holiday on a Monday, things would always take longer (higher volume of transactions, nothing was done on weekends so everything just accumulated). In situations where it was the end of a month AND a bank holiday on a Monday? Holy crap. I wouldn't get out of there until 4AM usually in those situations. There was a great deal of hand-holding and operator intervention during the processing. The systems used were older than many of the people working on them. When software updates needed to be made, companies had to locate retired software engineers that originally made the systems and pay them astronomical amounts to either perform the modifications or consult on such modifications. When hardware broke down, like our high-speed dot matrix printer that printed on that green-bar paper with holes on each side, they had to pay specialized repair techs $400+/hr (starting from when they got in their car in a city 1.5hr away) to come out to troubleshoot. Then they had to track down replacement parts. When you work with a bank, if something still functions, or the cost of repairing or updating it costs less than purchasing and transitioning to a new system, it does not get replaced. Systems ossify and live pretty much forever. The mainframe we used was literally the only one of its kind still in operation in the entire country (we found this out when the other people who used one, a restaurant, decommissioned theirs and gave it to us for free if we would hail it away... we finally got a disaster recovery solution that way).