What's not in your wallet is in a spreadsheet in what's called a core data center, a massive concrete building full of servers. But really, says information-security executive John Meakin, "your money is everywhere." Like credit-card companies and Wall Street brokerages, Meakin's London-based bank backs up information across data centers; his are in the U.K., Hong Kong, Kuala Lumpur, Singapore and Chennai, India. What he means by "everywhere" is that with ATMs and online banking, servers can deliver your money anywhere, anytime. But don't go on faith. As a financial citizen, it's important to understand how the digital bank knows what you're worth.