I imagine much of Visa's data centre capacity goes to serving web pages and all that. I know of a bank that would run millions of transactions per day in a coup

I imagine much of Visa's data centre capacity goes to serving web pages and all that. I know of a bank that would run millions of transactions per day in a couple of hours on an IBM mainframe (at night, after closing). While they are power hungry machines, I can't imagine them using 1MW. So I think 1.7Wh per transaction is at least an order of magnitude too high.