Dec 5, 2017

Mining Bitcoin on a 55 year old IBM mainframe works worse than expected

I ran into an interesting blog post today where a guy named Ken Shirriff decided to test what would happen if you mined Bitcoin on a 55 year old IBM 1401 mainframe! If you think he was able to really crank out hashes on that old giant monstrosity using punch cards and assembly language, well... you would be wrong.


The IBM 1401 can compute a double SHA-256 hash in 80 seconds. It requires about 3000 Watts of power, roughly the same as an oven or clothes dryer. A basic IBM 1401 system sold for $125,600, which is about a million dollars in 2015 dollars. On the other hand, today you can spend $50 and get a USB stick miner with a custom ASIC integrated circuit. This USB miner performs 3.6 billion hashes per second and uses about 4 watts. The enormous difference in performance is due to several factors: the huge increase in computer speed in the last 50 years demonstrated by Moore's law, the performance lost by using a decimal business computer for a binary-based hash, and the giant speed gain from custom Bitcoin mining hardware. 
To summarize, to mine a block at current difficulty, the IBM 1401 would take about 5x10^14 years (about 40,000 times the current age of the universe). The electricity would cost about 10^18 dollars. And you'd get 25 bitcoins worth about $6000. Obviously, mining Bitcoin on an IBM 1401 mainframe is not a profitable venture...
...Implementing SHA-256 in assembly language for an obsolete mainframe was a challenging but interesting project. Performance was worse than I expected (even compared to my 12 minute Mandelbrot). The decimal arithmetic of a business computer is a very poor match for a binary-optimized algorithm like SHA-256. But even a computer that predates integrated circuits can implement the Bitcoin mining algorithm. And, if I ever find myself back in 1960 due to some strange time warp, now I know how to set up a Bitcoin network.
Ken went on to say that he didn't actually mine real Bitcoin using this museum computer, but he did actually create and run the SHA-256 algorithm on the IBM 1401, showing that mining is possible in theory. He verified that he was able to find a successful hash by comparing it against one that had already been mined.

Line printer and IBM 1401 via
Even though it doesn't really make any sense to try and attempt mining on such old hardware, this little experiment is kind of fun an interesting in my opinion.

What do you think? Let us know in the comments!

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