IBM 604
IBM's first mass-produced electronic product: a calculating punched-card machine with fourteen hundred tubes, programmed by plugging wires into a board.
Introduced in 1948, it did essentially the job of the relay-based 601 — read two numbers off a card, compute, punch the answer into blank columns of the same card — but electronically, which left room for far more operations per card. The program was up to sixty steps wired on a control panel, and the machine ran at roughly a hundred cards a minute. There was no stored program: the shape of the calculation lived in the wiring, the data came out of the deck.
What mattered technically was not the speed but the maintenance. The roughly 1,400 tubes sat in pluggable modules of a couple of tubes each, so a failing circuit was swapped on the spot instead of traced component by component. That is what made vacuum tubes sellable to customers with no engineering staff of their own, and over 5,000 units were built.
Wired to a 402-series accounting machine, the 604 became the heart of the Card-Programmed Calculator — the product that brought engineering computation into ordinary companies a few years before an actual computer was something you could order.