This was the largest and most expensive dock for the PowerBook Duo and the only form factor offered exclusively by Apple. Unlike the other docks, or "port replicators" that plugged into the back of other laptops, the Duo Dock pulled the laptop inside the dock's metal and plastic case via an internal sliding mechanism (similar to that of a VHS player). The dock turned the PowerBook Duo into a full-size, AC-powered, fully functional desktop computer with all the standard ports.
[1]
Like a desktop computer, the dock could physically support a heavy, high-resolution CRT display on top. The Duo Dock included a
floppy drive on the side, two
NuBus expansion slots, an optional
floating point unit (FPU), level 2 cache, a slot for more VRAM to enable more colors at higher resolutions, and space for a second hard drive.
[1] The original Duo Dock was replaced by the Duo Dock II, which added
AAUI networking and compatibility with the newer color-screen PowerBook Duos. A replacement lid was offered to allow use of the thicker color Duos with the original Duo Dock. The Dock II was followed by the Duo Dock Plus, which was identical to the Duo Dock II, but lacked the FPU and level 2 cache—which were not compatible with the
68LC040-processor Duo 280 and PowerPC-processor Duo 2300c. 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.