The database system that sends Web surfers to the right page and gets e-mail messages where they need to go turned 20 years old on Monday. This follows Ethernet's 30th birthday last month.

DNS (Domain Name System) had its first successful test on June 23, 1983, at the University of Southern California School of Engineering's Information Sciences Institute (ISI), in Marina del Rey, California, said Paul Mockapetris, the researcher who invented the system. Jon Postel, another computer scientist at ISI, had assigned him to create a new kind of directory of the Internet, then a fledgling network of about 200 computers.

Before DNS, the addresses of all computers on the Internet were maintained in a central catalog of host names and addresses. Mockapetris devised a system that let those who had computers on the Internet own a domain and assign their own computers to it.

"Once you got your organization connected to the network, you could have as many computers on it as you wanted, and you could name them yourself," Mockapetris said.

With further refinement, it became the system of ".com," ".edu," ".gov" and other top-level domains still used by e-mail and Web users.

Mockapetris is now chief scientist and chairman of the board at IP (Internet Protocol) address software vendor Nominum Inc. and a visiting scholar at the university's Jon Postel Center for Experimental Networking, named for his former supervisor, who died in 1998.