A Single server is responsible for maintain the IP addresses and Host names for small regions. But when we use Domain Name System, it maps all the domain names to their IP addresses and this allows the computers to communicate across internet.
By using Domain Name System we can use simple names to the websites or by using IP addresses also we can access the websites. DNS is also broken up into multiple parts because servers are responsible to access small amount of data, every part we can call it as a zone.
A server that has authorization information about domain is called as Parent zone. DNS servers are configured by using multiple sub domains called as Child zone.