Although BIND is the most popular domain name server software being used today, NSD (“name server daemon”) is another popular alternative open-source server program.

NSD is an authoritative name server (i.e., not implementing the recursive caching function by design) and uses BIND-style zone-files (zone-files used under BIND can usually be used unmodified in NSD, once entered into the NSD configuration).

NSD uses zone information compiled via ‘zonec’ into a binary database file (nsd.db) which allows fast startup of the NSD name-service daemon, and allows syntax-structural errors in Zone-Files to be flagged at compile-time (before being made available to NSD service itself).

The collection of programs/processes that make-up NSD are designed so that the NSD daemon itself runs as a non-privileged user and can be easily be configured to run in a Chroot jail (A chroot environment can be used to create re-root a program to another directory in unix), such that security flaws in the NSD daemon are not so likely to result in system-wide compromise.

Most of the Internet root nameservers use BIND, however a few of them also use NSD. Apart from that several other TLDs use NSD for part of their servers.

Domain Name Servers on the internet use various software to function, the most popular DNS server type on the internet is BIND, which stands for Berkeley Internet Name Domain. BIND is the predominant system on UNIX based systems. 

BIND was originally created at the University of California, Berkeley and is maintained today by the Internet Systems Consortium. It was rewritten to address architectural difficulties and also to support DNSSEC (DNS Security Extensions).

BIND initially supported only flat text files to store and retrieve data. However, recent versions of BIND have allowed zone data storage and retrieval in a variety of database formats including LDAP, PostgreSQL, MySQL, and ODBC.

Since BIND was written a long time back, there were many security vulnerabilities that have been exploited by earlier versions of BIND and hence their use is strongly discouraged. The latest version of BIND should be deployed, although they have also experienced numerous vulnerabilities which can be managed to some extent by using DNSSEC and other technologies

More information about BIND at the ISC website can be obtained from https://www.isc.org/software/bind