In October 1984, RFC 920 set out the creation of ccTLDs using country codes derived from the corresponding two-letter code in the ISO 3166-1 list. "GB" is the UK's ISO 3166 country code. However, the UK academic network Name Registration Scheme, JANET NRS, had defined "UK" as the top-level domain a few months before the compilation of the ISO-derived list. Consequently, .uk was chosen and registered on 24 July 1985. .gb was reserved but never widely used and it is no longer possible to register domains under that ccTLD.