This document discusses personal digital assistants (PDAs). It begins by defining a PDA as a portable, pocket-sized organizer and computer. It then discusses some of the early PDA manufacturers like Apple and how their features have developed over time from early touchscreen and memory card models to today's wireless connected smart devices. The document also outlines some common PDA applications like calendars, notepads, address books and games as well as their use by medical, scientific and other mobile professionals. It concludes with some limitations of early PDAs related to size and data input/output speeds.