After further review, rather than skipping every other cylinder, like I put in the commit, it looks to be treating the disk as having one side but double the number of cylinders. By that I mean when it wants to read cylinder 0 head 1 the BIOS tells the FDC it wants cylinder 1 head 0 or for cylinder 5 head 1 it asks for cylinder 11 head 0 and so on. I'm not sure of the cleanest way to emulate that.
