Story on DNS Root Servers
"The eight U.S. gTLDs are all currently operated by Network Solutions and run on IBM AIX servers using the same software. As with root servers, there are also international gTLDs, located in Hong Kong, Tokyo, Stockholm, and the U.K. The gTLDs get many more requests than the root servers and are in fact more critical to DNS operation. The root servers simply point to the gTLDs and ccTLDs. These servers, in turn, return the addresses of the authoritative name servers for most domains."