On Unix, there was the "talk" command for split-screen chat, and also "write" to just send a message to someone else's terminal subject to permission with the "

On Unix, there was the "talk" command for split-screen chat, and also "write" to just send a message to someone else's terminal subject to permission with the "mesg" command. Not all systems had such provisions (or, in come cases, they had to be written by users).