- The IBM 604 Electronic Calculating Punch (1948) was a programmable calculator bridging electromechanical and electronic computing.
- It was smaller and cheaper than contemporary computers, using vacuum tubes for faster operations like multiplication and division.
- The 604 introduced pluggable modules for vacuum tubes, simplifying maintenance and enabling mass production.
- Thyratron tubes in the 604 acted as high-current switches, staying on until power was cut, used for driving relays and card punches.
- Despite lacking stored programs and loops, the 604 was highly successful with over 5600 units produced, leading to later IBM computers like the IBM 650.