Mining Bitcoin On The 15-bit Computer That Brought Man To The Moon

The computer that brought American astronauts to the Moon and calculated their return trajectory has a new use. Experts tried to reprogram it to mine Bitcoin. While the 50-year-old computer can't really compete with new specialized machines it was an interesting experiment.

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In the year 1969 – fifty years ago – the computer named AGC (Apollo Guidance Computer) had a key role in the return maneuver of Apollo 11. This computer is often called upon when we compare how far have computer progressed since then. You can often hear: „Nowadays you have a million times more powerful computer in your pocket than the astronauts had when they landed on the Moon.“ And as the fiftieth anniversary of Moon landing a few computer historians had an idea – they will repurpose the AGC. And so it wouldn't be a complete waste of time, they decided to have it mine Bitcoins.

To some of you, mining Bitcoin on a computer from the sixties might sound like a crazy and stupid idea. But that was exactly why Ken Shirriff decided to try it. Through homemade circuits, he connected the AGC to the internet so mining could begin. Theoretically, all that was left to do was to give the computer some mining software. But coding that wasn't easy. The hash algorithm SHA-256 that is used to mine Bitcoin uses 32-bit operations. But the AGC used a 15-bit architecture so each 32-bit operation requires three different operations on the AGC (one 4-bit operation and two 14-bit operations).

Another problem was with capacity. AGC had a memory of just two thousand commands – roughly 4 thousand bits. And standardly the programmer had access to only 256 of those commands. The SHA-256 algorithm used 240 of those commands which meant that only very few were left for anything else. Also, the AGC didn't have certain operations available so Sherriff needed to code them into specialized subroutines making the calculations even slower.

But in the end, they managed to get the mining work. But it's really not profitable. It takes about ten seconds for a single hash to be calculated by AGC. In comparison, a specialized Bitcoin mining machine is about a trillion times faster. And even mining on a regular notebook would be a hundred times quicker.

Sources:

• https://arstechnica.com/tech-policy/2019/07/computer-from-nasas-apollo-program-reprogrammed-to-mine-bitcoin/

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