>a database small enough to be served from a computer from the 90s?

Putting ~170 million .com records into a RDBMS on a 90s computer is not enough infrastructure to serve ~746 billion DNS queries a day : https://www.verisign.com/about-us/

They don't use off-the-shelf Redis/PostgreSQL/MySQL and they have more uptime reliability than Github, AWS us-east-1, Anthropic Claude, etc.

Verisign may still overcharge for what they do but nevertheless, the computing infrastructure isn't trivial.