with a view to supporting the planned major expansion program, a new prestel infrastructure was designed around two different types of data center: update centre (udc), where ips could create, modify and delete their pages of information, and information retrieval centre (irc), which mirrored copy of the pages is provided to end-users. in practice there only ever was one update centre, 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.