The Slot A connector allows for a higher bus rate than Socket 7 or Super Socket 7. Slot A motherboards use DEC's EV6 bus protocol, a technology that was originally developed for the Alpha 21264 processor.
Slot A is mechanically compatible but electrically incompatible with Intel's Slot 1. As a consequence, Slot A motherboards were designed to have the connector's installed orientation be rotated 180 degrees relative to Slot 1 motherboards to discourage accidental insertion of a Slot 1 processor into a Slot A motherboard, and vice versa . The choice to use the same mechanical connector as the Intel Slot 1 also allowed motherboard manufacturers to keep costs down by stocking the same part for both Slot 1 and Slot A assemblies.
Slot A was superseded by Socket A.