From Ken Shirriff’s blog
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.
You might think that Bitcoin would be impossible with 1960s technology due to the lack of networking. Would one need to mail punch cards with the blockchain to the other computers? While you might think of networked computers as a modern thing, IBM supported what they call teleprocessing as early as 1941. In the 1960s, the IBM 1401 could be hooked up to the IBM 1009 Data Transmission Unit, a modem the size of a dishwasher that could transfer up to 300 characters per second over a phone line to another computer. So it would be possible to build a Bitcoin network with 1960s-era technology
Bitcoin, a digital currency that can be transmitted across the Internet, has attracted a lot of attention lately. If you’re not familiar with how it works, the Bitcoin system can be thought of as a ledger that keeps track of who owns which bitcoins, and allows them to be transferred from one person to another. The interesting thing about Bitcoin is there’s no central machine or authority keeping track of things. Instead, the records are spread across thousands of machines on the Internet.
The difficult problem with a distributed system like this is how to ensure everyone agrees on the records, so everyone agrees if a transaction is valid, even in the presence of malicious users and slow networks. The solution in Bitcoin is a process called mining—about every 10 minutes a block of outstanding transactions is mined, which makes the block official.
More details HERE