Vacuum-tube computers, now called first-generation computers, are programmable digital computers using vacuum-tube logic circuitry. They were preceded by systems using electromechanical relays and followed by systems built from discrete transistors. Often vacuum-tube computers made extensive use of solid-state ("crystal") diodes to perform AND and OR logic functions per diode-resistor logic (DRL) also diodeâÂÂtransistor logic (DTL), and only used vacuum tubes to amplify signals between stages or to construct elements such as flip-flops, counters, and registers. The solid-state diodes reduced the size and power consumption of the overall machine. Some later computers on the list had both vacuum tubes and transistors.
This list of vacuum-tube computers is sorted by date put into service, and notes the vacuum tube:Crystal diode semiconductor (VT:CD) ratio, e.g., "747 V : 10,500 D" for SEAC (computer):