message frame, although some popular micro-computers of the time provided the facility to store the message so that it could be copied and pasted into a new message. Special commands were also available. For example, to facilitate movement around the database it was possible to step back through a maximum of 3 frames or pages by use of the special key combination "*#". In the event of corruption of a page in transmission it was possible to refresh the page by means of the code *00, which had the advantage of avoiding any page charge being raised again. Alternatively, if the user wished to update a page to see the latest information, for example of flight arrival times, the *09 command would retrieve the latest updates, at the same time re-billing any page display charge. If all else failed, a user could simply return to the first page which he saw after logging onto the system by use of the *0# combination, which brought up their default Main Index. Exceptionally, information could be hidden on a frame by an IP which could only be revealed by use of the 'Reveal" key of the keypad (e.g., to show an answer to a quiz). The same 'Reveal' key was also used to hide the data once more. Infrastructure With a view to supporting the planned major expansion programme, a new Prestel infrastructure was designed around two different types of data centre: 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. In those early days of the public service all the live Prestel computers were located in St Alphage House, a 1960s office block on Fore Street in the City of London. At the time the National Operations Centre (NOC) was located in the same building on the same floor. The computers and the NOC were later moved to Baynard House, (on Queen Victoria Street, also in the City of London) which acted as a combined UDC and IRC. Both types of machine, together with other development hardware, remained in service there until 1994 when the Prestel service