Ken Shirriff did an in-depth write-up of the punched card sorter:
Punched card sorters were a key part of data processing from 1890 until the 1970s, used for accounting, inventory, payroll and many other tasks. This article looks inside sorters, showing the fascinating electromechanical and vacuum tube circuits used for data processing in the pre-computer era and beyond.
More details at Ken Shirriff’s blog.
Check out the video after the break.