There have been three eras of general computing… the fourth remains to be written. A highly-compressed overview of the history of general computing The first era of general computing was the mainframe era and it was centralised. The second, the personal computing (PC 1.0) era, was decentralised. The third is the Web era (let’s call it Mainframe 2.0). And it is, once again, centralised. Today, we find ourselves at the end of the Mainframe 2.