The EX and HX are upgradable via Tandy PLUS cards, and these systems have bays for three cards. A PLUS card connector is electrically identical to an ISA slot connector, but uses a Berg-style 62-pin connector instead of a 62-contact ISA card-edge connector. Other PLUS cards could be installed to add serial ports, a 1200-baud modem, a clock/calendar and bus mouse board, or a proprietary Tandy network interface. Radio Shack later sold an adapter card allowing installation of a PLUS card into a standard ISA slot, such as those in the larger Tandy 1000 models.