V10-13 represented virtual disk images on a hard drive, each partition exactly one floppy in size.
As I have time, I will sift through the code and perhaps leave some comments here.
To start, the copy protection source code on Disk 4 is interesting. :)
I'm also a bit fond of the font rendering code on disk 1... S_FDRAW.txt Check out the procedural kerning! We sure put the 6502 through its paces.