Which two program alarm codes appeared during Eagle's descent?

The two program alarm codes that appeared during Eagle’s descent were 1201 and 1202. They signaled that Apollo 11’s guidance computer was overloaded, but its priority-based software preserved the tasks needed to land.

The alarms were caused by an unexpected stream of computer work associated with the lunar module’s rendezvous radar, which was tracking the command module Columbia overhead. A display command entered by Buzz Aldrin added still more workload, producing repeated 1202 alarms and a 1201 alarm during the descent.

Mission Control engineer Jack Garman and guidance officer Steve Bales quickly recognized the alarms and determined that Eagle could continue. The computer automatically discarded lower-priority tasks and restarted in a way that retained critical guidance and control functions. Bales therefore gave the famous “GO” decision rather than ordering an abort.

The numbers are sometimes misremembered as ordinary error codes or as evidence that the computer had failed. They instead described executive-overflow conditions: the computer was temporarily asked to do more work than its normal capacity, but its design allowed it to recover and keep flying the mission.