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.