[5] Its primary purpose was to ensure a standardised and organised approach to domain name registration, facilitating identification and differentiation of institutions and their computer resources on the network.
NRS "second-level domains" consisted of UK.AC (JANET academic and scientific sites), UK.CO (commercial) and UK.MOD (Ministry of Defence).
Any organisations not falling into these categories were given their own "second-level" name, e.g. UK.BL (British Library) or UK.NEL (National Engineering Laboratory).
[2][3][6][7] As Internet usage expanded and commercial entities emerged, the more general Domain Name System (DNS) superseded the NRS.
The one remaining legacy of the NRS is the convention of using .uk for the Internet country code top-level domain (ccTLD), rather than .gb as specified by ISO 3166.