In the early days of the Internet, there was just a single file that held the addresses of all host computers on the Net. Logically called the host table, it was updated only a couple of times a week, as new computers were connected to the Internet. Then Internet growth exploded. The people who maintained the host list got swamped. This distributed arrangement could handle any amount of growth.
Name servers are like telephone directory assistance operators.
An operator takes a name and gives you the telephone number you need to dial to reach a person or business. Nearly every ISP has some sort of name server, and your browser first checks with the one closest to you. Because new Web sites are added to the Internet constantly, not all name servers have complete information. Back to Dot Com. These are called top-level DNS names.