NASA's Apollo 11 onboard computer really was as primitive as they say

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IT'S ONE of the biggest tropes linked to the moon landings - that moment in the conversation when someone pipes up with the fact that the ship's computer was less powerful than a mobile phone.

But what does that mean exactly? What was the computer that took us to the moon like?

The first thing to say is that, yes, the facts are true, the Apollo Guidance Computer (AGC) was indeed less powerful than a mobile. In fact, it has about the same compute power as an Apple II, which would go on sale in 1977 for a cool $1298, boasting just 4KB of RAM.

That's quite a lot less than a mobile phone.

But let's just think about that for a moment - Apollo advances meant that we were able to buy a home computer, as powerful as NASA's. a mere eight years after the moon landing. That's pretty cool, and a reminder of the positive side-effects of the Space Race.

ACG was the first computer to use integrated circuits, which have become the norm for modern computing.

Yet, despite this, the AGC did most of the heavy lifting, with manual override controls only whipped out for the lunar landing itself. This was a major step up from Gemini and Mercury, most of which had to be piloted manually.

Astronauts could programme the computer with the interface, known as DSKY (say it ‘Disky'). There were only numbered keys, with a helpful legend printed on the side of the cabin to remind the three intrepid astronauts how to give it commands. The calculator style layout would later become the norm for domestic calculators.

Three DSKY interfaces were linked to Apollo XI - two in the command module, with a further one in the lunar lander.

The processor ran at a feeble 2.048Mhz (compare that to the 2Ghz on your phone), and the 15-bit RAM (with 1 parity-bit) used a combination of a magnetic core which could hold 2048 words and the core-rope (ROM) which held 36,384.

Two additional computers were also used - the LVDC to programme the Saturn V booster, and the AGS which would kick in if the lunar landing/takeoff needed to be aborted. If the AGS kicked in, the astronauts knew that their mission had changed from landing on the moon to getting home alive.

If all that has made you think, "well if its that easy, why haven't we been back yet", then go for your life - the source code for the ACG is available in its entirety on Github.

Bring us back a moon rock, yo? μ