Typically, a machine would feature multiple bus expansions slots, if any. However, there was never more than one PDS slot. Rather than providing a sophisticated communication protocol with arbitration between different bits of hardware that might be trying to use the communication channel at the same time, the PDS slot, for the most part, just gave direct access to signal pins on the CPU.
The one notable exception to this was the PDS design for the original Motorola 68020-based Macintosh LC. This was Apple's first attempt at a "low-cost" Mac, and it was such a success that, when subsequent models replaced the CPU with a 68030, and later even a 68040, and later even a PowerPC processor ways were found to keep the PDS slot compatible with the original LC, so that the same expansion cards would continue to work.
Mac portable challenges card makers; external networking solution may be necessary. (Apple's Macintosh portable)
Jan 11, 1990; Mac portable challenges card makers CUPERTINO, CA--Several companies that have engineered networking boards for the Macintosh II,...
An Apple turnover with Mac filling: the Apple IIe card. (terminal emulation card makes Macintosh LC run like an Apple IIe) (Hardware Review) (evaluation)
Sep 01, 1991; Can something be one small step backwards and an immense leap forward at the same time? The contradiction may seem confusing, but...