By now, a distinction had emerged between "internet" with a small i, and "Internet" with a capital I Officially, the distinction was simple: "internet" meant any network using TCP/IP while "Inter net" meant the public, federally subsidized network that was made up of many linked networks all running the TCP/IP protocols. Roughly speaking, an "internet" is private and the "Internet" is public. The distinction didn't really matter until the mid-1980s when router vendors began to sell equipment to construct private internets. But the distinction quickly blurred as the private internets built gateways to the public Internet.

— Where Wizards Stay Up Late di Katie Hafner (Pagina 242)