What are retrieval computers?

Some articles on computer, retrieval computers, computers:

Prestel Infrastructure
... programme, a new Prestel infrastructure was designed around two distinct types of computer centre the Update Centre (UDC) where IPs could create, amend and delete their pages of ... and this always housed just one update computer, named "Duke", but within six months of public launch there were in addition two dedicated information retrieval computers ... In those early days of the public service all the live Prestel computers were located in St Alphage House, a 1960's office block on Fore Street in the City of London ...