Nice video celebrating the IBM 1401 via Timothy Sipples who writes:
The IBM 1401 was so wildly popular that IBM provided optional 1401 emulation on the System/360 mainframes that were announced in 1964. Although it's hard to be certain, it is conceivable (and likely) that, somewhere, there are still programs originally written for the IBM 1401 that are running on today's System z mainframe, nearly 50 years on. Perhaps they've been modified and updated along the way, as business rules and other business needs evolved, but they were born many decades ago.
What an amazing journey.