So what is the Z80 card for?
Apparently for running CP/M on a PC.
http://books.google.com/books?id=gD4EAAAAMBAJ&pg=PA1
http://books.google.com/books?id=NjAEAAAAMBAJ&pg=PA1
http://pctimeline.info/ibmpc/index.htm
1982 March
Xedex introduces the Baby Blue card (a Z80B processor on a plug-in
card), allowing the IBM PC to run standard CP/M programs. Price:
US$600. [346.92] [396.10] (April [9]) (Vendex company[346.93])