[Animats]

This is batch processing. Many systems today, especially ones that process money, still look much like that. The hardware is different but the concept remains. Sequential files are created, sorted, merged, and outputs generated.

It's a reliable, well-understood process. If something funny happens, somewhere there is a logged transaction that made it happen. You don't just have an inexplicable database state. Auditors look for those transactions that made something funny happen. What you see in online banking is often yesterday's batch run plus interim updates during the day. The real updates happen in some batch job.