The Internet uses a naming system called the Domain Naming System (DNS).
The DNS system allows us to refer to computers and other devices (routers), with names (domain names) and not the IP address (Internet Protocol address) which is difficult to remember and uncomfortable to use. For example, it is easier to remember iguru.gr than 220.127.116.11.
DNS is responsible for converting domain names to the relevant IPs. If you are currently using automatic server selection DNS using your system, you will use the servers DNS automatically assigned by your ISP (your ISP).
These DNS may be the fastest DNS servers available. It can even be in the wrong order (the second is faster than the first and that matters).
The DNS Benchmark application will show you what happens to the DNS servers assigned to your system by automatically comparing their performance with many known alternatives.
The GRC DNS Benchmark application performs a detailed analysis and comparison of operational performance and reliability from 200 DNS nameservers simultaneously.
When Benchmark starts at its default setting, it identifies all the DNS name servers that the user's system has and adds them to the built-in list of available alternative name servers.