The Franklin REX 5, was one of the Rex line of Personal Digital Assistants, each a PCMCIA PC card and thus the size of a credit card, built around a Toshiba microprocessor emulating a Zilog Z80. The REX firmware was written by Starfish Software, and the hardware was manufactured by Citizen Electronics. Earlier models in this line had almost no input possibilities except to download data when installed in a host computer or in a docking station; the Rex 5 added a sixth button and introduced a modal input method. Further, with 512 KB of RAM, the Rex 5 had twice the memory of the Rex-3.