>>> When DOS detects an unreliable floppy change line hardware,
>>> it should use the floppy label / serial / similar to detect
>>> changes in software ...
>> How does DOS ever detect that any hardware is "unreliable"??
> I do not know, but earlier in this thread, somebody said that
> the numbering of FAT filesystem exists, among other reasons,
> to help DOS detect floppy changes even if there is no change
> line available. As you know, int 13.15 can even report that
> a floppy has no change line at all. MS DOS might, on top of
> that, have a list of BIOS versions with "weak" change lines?

I think this excerpt might be relevant; from Geoff Chappell's "DOS  
Internals", chapter 16 ("Low-Level Disk Support"), after the section  
heading "Floppy Disk Drives", on page 605:

As a normal part of its initialization, IO.SYS categorizes the available  
floppy disk drives. For this purpose, it relies on the BIOS to report the  
drive's capabilities. Int 13h function 08h (Get Drive Parameters) returns  
the maximum supported values for the cylinder, head and sector parameters.  
In the context of assigning drive types, it is sometimes helpful to know  
whether or not the BIOS supports "change-line" detection (i.e., the drive  
can detect whether the drive door is open) for the drive in question. One  
indirect inference is available since the low-capacity 5 1/4 " drives are  
unable to provide a change-line facility.

It doesn't go into more details regarding the change-line detection  
support detection right there, but I'll report in another reply (to this  
message) if I find more elsewhere.


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