ITS was used mostly in the era before DNS, when a hosts.txt file was regularly distributed to all Arpanet hosts. If you want to add a new host and its IP number, you have to update ITS' host table.
ITS' human readable host table is in the file
SYSHST; H3TEXT >. You update it with a regular text editor. To add a new host, enter a line like
HOST : A.B.C.D : NAME : MACHINE : OS : :. A.B.C.D is the IP number, and NAME is the hostname. MACHINE and OS are free text descriptions.
Having done this, you have to update the binary host table
SYSBIN; HOSTS3 > which is what programs actually use to look up host names. To update this from the text file, just run