Today it’s 31 years since Microsoft finalized the purchase of 86-DOS, also known as QDOS, or Quick and Dirty Operating System. This was the operating system that would be installed on the first IBM PC, introduced in August 1981.

The rest is history, as they say. If you would want to relive the good – ahem – old days of DOS before it was even called MS-DOS, here’s how you can.