The roar of the Zambezi is deafening as millions of gallons of water crash over rocks and tumble down rapids.

But there's another sound cutting through the trees of the Zambian bush - the unmistakable high-pitched whine of a bitcoin mine.
"It's the sound of money!" says a smiling Philip Walton as he surveys the shipping container with 120 computers busily crunching through complex calculations that verify bitcoin transactions.
In exchange they are automatically rewarded bitcoin by the network.