The Real-Time Computer Complex (RTCC) was an IBM computing and data processing system at NASA's Manned Spacecraft Center in Houston. It collected, processed and sent to Mission Control the information needed to direct every phase of an Apollo/Saturn mission. It computed what the space vehicle was doing and compared that with what it should be doing. RTCC worked in real-time -- so fast, there was virtually no time between receiving and solving a computing problem.
IBM 7094-11 computers were used in the RTCC during NASA's Gemini program and on the first three Apollo/Saturn missions. Later, IBM System/360 Model 75J mainframes, plus peripheral storage and processing equipment, were employed. Two computers were used during a mission: one was primary; the other operated identically but as standby.