A: RDAP delivers registration data like WHOIS, but its implementation will change and standardize data access and query response formats. Additional advantages over WHOIS include support for internationalization, secure access to data, and the ability to provide differentiated access to registration data.
Historically, registrars have been required to provide public access to data associated with registered gTLDs (domain creation date, domain owner contact details, name servers). This data is often referred to as the “WHOIS” of a domain name, and registrars provide access to WHOIS through an interactive web page that queries from their database, commonly referred to as “port 43”. This requirement was per contractual obligations of ICANN's Registrar Accreditation Agreement (RAA).