provided via the duplex asynchronous interface provided by banks of GEC 16-port multi-channel asynchronous control units (MCACCU) known more simply as multiplexers. These devices in turn were accessed via banks of standard Post Office Modems No. 20 operating at 1200/75 bit/s, which were connected directly to the public switched telephone network (PSTN). As seen in 1979, it had important strengths and weaknesses: "The strengths of viewdata include its visual attractiveness, its ease of use, low cost and its wide range of applications. Its weaknesses include its small information window, unsophisticated search methods, its limited storage capacity and its lack of computer power for users. How rapidly viewdata will become established, and the exact role it will fulfil, is as yet a matter of speculation." By 1981, this configuration had changed with memory doubled to 768 kbytes but with data discs reduced to six, corresponding to the number at the IRC machines and with just a single transaction disc. In addition to the MCACCU units required to support 1200/75 dial up access, the Update Centre machines were also connected to special modems provided to support online bulk updating by IPs. Banks of 300/300 bit/s full duplex asynchronous V21 modems supported computer to computer links for the more sophisticated IP while 1200 bit/s half duplex V23 modems supported so called intelligent editing terminals (i.e. those capable of storing a number of frames offline before uploading to the UDC). In addition twin 9-track NRZI tape decks of 800 bytes/inch capacity were provided in order to support bulk offline updates. Although technically categorised as minicomputers, these GEC machines were physically very large by today's standards, each occupying several standard communications cabinets, each standing high by wide. The CDC 9762 hard disc drives were housed separately in large stand-alone units, each one about the size of a domestic washing machine. (See images in the photo of the GEC Computers' Development Centre). The 70 Mbyte capacity hard discs themselves were in fact removable units, each consisting of a stack of five 14-inch platters, standing high, that could be lifted in and out of the drive unit. The GEC machines cost in excess of £200,000 each at GEC standard prices, in addition to which there were the costs of all the associated communications equipment. Putting together all of the computer and communications equipment required for a single IRC was a major undertaking and took some 15 months