the 8088 can support 64k ports, so logically the lower
16 address lines would be utilized to address them.
A16-19 were multiplexed with other pin functions. IIRC
the pc only allows for 256. Probably a good book on
the topic is Interfacing to the IBM PC by Eggebrecht
(Sams). Dont rely on that being the exact title or the
way the authors name is spelled. Chances are its
available on Amazonia for a song.
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