Josh Bensadon originally wrote the Z80MC's CP/M code for his JAIR board. It's a single-board S-100 computer with an 8080 CPU, 64k RAM, boot ROM, 2 serial, 3 parallel ports, and a parallel interface to an SD-card serving as its "disk" drive. He noted that the 2 MHz 8080 parallel interface was about the same speed as the 4 MHz Z80 with "bit banged" SD-card interface. So that's what we went with for the Z80-SIO.
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It's not as fast as modern hard drives, but is certainly faster than any floppy disk system I've had. CP/M programs also tend to be small, so disk read/write time is not nearly as important as you might expect.
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Josh used FAT16 so you could read/write/format the SD-card on a PC. It does slow down the Z80 to read the FAT16 directory structure instead of the simpler CP/M structure, but was a straightforward way to allow up to a 2 Gb disk.
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Lee
--
Excellence does not require perfection. -- Henry James
But it *does* require attention to detail! -- Lee Hart
Lee Hart