PC World has a great article about ancient computers still being used today. For example, Sparkler Filters of Conroe, Texas, uses an IBM 402 from 1948 for all of their accounting and billing tasks:
Of course, before the data goes into the 402, it must first be encoded into stacks of cards. A large IBM 029 key-punch machine–which resembles a monstrous typewriter built into a desk–handles that task.
Carl Kracklauer, whose father founded Sparkler Filters in 1927, usually types the data onto the punch cards. The company sticks with the 402 because it’s a known entity: Staffers know how to use it, and they have over 60 years of company accounting records formatted for the device.
The key punch isn’t the only massive accessory in Sparkler’s arsenal. The 402 also links to an IBM 514 Reproducing Punch, which has been broken for three years. When it works properly, the 514 spits out punched “summary cards,” which typically contain the output of the 402’s operation (such as sum totals) for later reuse. Sparkler stores all of its punched data cards–thousands and thousands of them–in stacks of boxes.
The company also possesses dozens of 402 programs in the form of IBM plugboards. Computer programming in the 1940s commonly involved arranging hundreds of individual wires in a way that would likely drive a modern software engineer insane. In the 402’s case, a spaghetti-like pattern of wires attached to hundreds of connectors on each plugboard determines the operation of the machine, and different plugboards can be pulled out and replaced as if they were interchangeable software disks. So you might insert one plugboard for handling, say, accounts receivable, and a different one for inventory management.