"This item is backplane for Zorro I expansion cards (also works with Zorro II, though you plug them in backwards) for the Amiga 1000. These were built by the Amiga group in Los Gatos, basically as a proof of concept for the Zorro bus. This backplane is supposed to be powered by a separate power supply (via the connector at the bottom), but it has been modified to run with the A1000's own power supply. " - Dave Haynie

Officially, there's no such thing as Zorro I. However when Zorro II was released, the side expansion slot on the A500 and A1000 was retrospectively referred to by some as a Zorro I slot (albeit incorrectly). In other words, it appears to be an adaptor which is designed to extend the side expansion slot of the A1000 into a series of "Zorro I" backplane slots. Apparently the card can also be plugged into a genuine Zorro II slot to provide the same functionality.

Thanks to Dave Haynie