(5) Human interface DSKY

Description and some techy stuff about the DSKY of the Apollo Guidance Computer (AGC):  [index]

The DSKY (display and keyboard) is the unique direct human interface of the Apollo Guidance Computer (AGC). Two DSKYs are connected to the AGC in the command module, a third to the AGC in the lunar landing module. I specifically emphasize “direct” interface, because the AGC’s were connected to many parts of the command or landing module for controlling and receiving information, and were sending information to mission control on earth from where extra input could be made. The AGC’s were far from autonomous closed boxes, rather the heart and brain of a hugely complex body!

In the 1960’s when the AGC was conceived, and still in 1969 when the first manned landing took place, the human interface with computers on earth was really no different. The HP2116 compared in this project, and the P82 quite some years later were using their own forms of “DSKY” for telling the computer what to do and getting responses back on lights, numeric displays, or maybe a Teletype, before the evolution of screens and graphic capabilities.

Yes, we had punched cards, paper tape and magnetic tape, and huge line and page printers as big and heavy as the moon lander module itself – but it would be more than 10 years before the individual human could easily be ‘heard and spoken to’ by the computer!


Behind the DSKY is an unimaginable complexity to light up “simple” numeric digits.

The most common displays at that time were “Nixie” displays (cold cathode tubes) used in instrument displays and would not have met power consumption nor vibration requirements suitable in space.

It should be mentioned that LED displays were just becoming a reality at that same time. In February 1969, Hewlett-Packard introduced the first LED device to use integrated LED circuit technology.

It was the first intelligent LED display, and was a revolution in digital display technology, replacing the Nixie tube and becoming the basis for later LED displays. The P82 uses 3 numeric & 1 Hexadecimal HP displays – shown here.

So imagine the challenge in 1963 of simply displaying numeric information! The solution was to develop a set of electro-luminescent markings of 7 segments each and a switching matrix driving 2-state latching mechanical relays. All this multiplied by 21 digits. That description alone makes the mind of today ‘boggle’.

Yet it worked, despite relays are expensive and their reliability doubtful, and a huge part of the DSKY space is taken up by relays and their drivers: 132 relays = 5 relays per 7-segment digit = 110 + 6 for sign + 15 for fixed lamps (left panel plus computer activity), + last one for static prog/verb/noun/lines. = 132. CuriousMarc’s video shows the situation. He and the team have built a relay switching matrix for a real AGC DSKY (see their video below) – so we can witness this amazing display quality, better than anything else around at that time.