What year is called the "birth of the Internet" when ARPANET switched to TCP/IP?

1983 → tub · foam.

On 1 January 1983 ("flag day"), ARPANET switched wholesale from its old NCP protocol to the TCP/IP suite designed by Vint Cerf and Bob Kahn — the moment separate networks could reliably interconnect into one "network of networks", which is what the word Internet literally means. TCP/IP's genius is that it makes no assumptions about the underlying wires, so any network that speaks it can join. The Domain Name System — the phone book turning names like example.com into addresses — also arrived around this time to cope with the growing network. Peg 19 · 83 → tub · foam: foam bubbling in a tub.