Improving upon the PowerBook 100's portability (its immediate predecessor and Apple's third-smallest laptop), the Duo came in seven different models.

The Duo line offered an ultraportable design that was light and functional for travel and expandable via its unique docking connector.

[1] Like a desktop computer, the dock could physically support a heavy, high-resolution CRT display on top.

While the laptop's LCD display obviously could not be opened when inside the dock, additional NuBus video cards could be installed to drive up to three monitors.

[14] The Mini Dock was a port expander for the PowerBook Duo and was popularly offered by many third-party manufacturers and Apple.

Third-party contributions to the Mini Dock added a variety of specialized custom options including Ethernet connectivity, NTSC and PAL video ports.

This type of dock was manufactured by both Apple and many third parties, and gave the PowerBook Duo up to three extra ports in a minimal configuration.

Popular due to the minimal impact in accessories that must be carried with the Duo, they offered a practical alternative to emergency hard disk and software situations and task-specific needs.

In addition to the Snow White features, the Duo takes the 100's radius curves a step further along the display top, front, and sides, and which is also heavily mirrored in the various docks.

[15] The PenLite was based on the PowerBook Duo and was meant to be a tablet-style addition, with a stylus as the input device.

It was designed to be compatible with PowerBook Duo docks and accessories[16] and ran the standard classic Mac OS.