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An old IBM mainframe was setup with the SHA 256 hashing algorithm. It took around 80 seconds to complete one hash. To put that in perspective most ASICs hit around a trillion or more hashes per second.
Could an IBM mainframe from the 1960s mine Bitcoin? The idea seemed crazy, so I decided to find out. I implemented the Bitcoin hash algorithm in assembly code for the IBM 1401 and tested it on a working vintage mainframe. It turns out that this computer could mine, but so slowly it would take more than the lifetime of the universe to successfully mine a block. While modern hardware can compute billions of hashes per second, the 1401 takes 80 seconds to compute a single hash. This illustrates the improvement of computer performance in the past decades, most famously described by Moore's Law.
http://www.righto.com/2015/05/bitcoin-mining-on-55-year-old-ibm-1401.html
