In my quest to preserve retrocomputing documents, here is the invaluable book “Inside Commodore DOS”, which describes most of the internals of the Commodore 1541 disk drive. The scanning was done in 2002 by Kenneth S. Moore, who in 2005 released an OCRed version, which unfortunately replaced the original page images. My version here comes with the original page images and a table of contents, and is nevertheless fully searchable.
Here is a fun quote from the book by the way:
Over the years numerous writers have advised Commodore owners not to use the save and replace command because it contained a bug. Our study of the ROM routines and a lot of testing has convinced us that the bug in the replace command is a myth.
Of course, this is wrong. Don’t use “SAVE@” on a 1541.