The Portables are the oldest computers from Compaq, they were the first luggable pc's. They were designed to compete with IBM and in some cases were more compatible with IBM software than IBM PC's. That was certainly the case with the IBM Portable and the IBM PS/2.
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Compaq also sold different devices with the same goal, making the pc experience portable. They created the iPaq pda's, tablet pc's (like the Concerto) and handhelds.