80 seconds per hash:-)
Great piece by Ken Shirriff
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 thanks to 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 5x1014 years (about 40,000 times the current age of the universe). The electricity would cost about 1018 dollars. And you'd get 25 bitcoins worth about $6000. Obviously, mining Bitcoin on an IBM 1401 mainframe is not a profitable venture.