Back in 1981, when the internet was little more than an experiment, Internet Protocol Version 4, or IPv4, was created, in which every computer's identifying address is 32 bits long, allowing for a grand total of about 4.3 billion different addresses. These are typically shown as the IP address we're all used to: Four numbers, each ranging from 0 to 255, separated by dots. PopSci.com is 18.104.22.168. The 32-bit length was basically arbitrary--Vint Cerf, who chose that length all those decades ago, said in an interview, "Who the hell knew how much address space we needed?" More than 4.3 billion, it turns out. ICANN, a group set up by the U.S. Department of Commerce, hands out IP addresses in large clumps to regional internet registries, or RIRs, which represent different parts of the world. Those RIRs then lease their addresses to ISPs, both home (like Comcast) and mobile (like Verizon Wireless).