Personal Digital Assistant: A handheld computer that can be used for simple Personal Information Management (PIM) functions. As PDAs have become increasingly sophisticated, some are poised to usurp the place of subcompact notebook computers, and can be used for more complex functions such as viewing and editing documents, spreadsheets, and presentations. PDAs run on a variety of Operating Systems (OS), the most common of which are the Palm, Microsoft Pocket PC, Symbian, and Linux.