To: Green Dragon #35 @1916006
Subject: Probable non-DOS disk

GD>What do you do to correct a disk when it says: "Probable non-DOS disk"
  >when I chkdsk the drive?  It's a DBLSPACEd drive & it just popped up
  >somehow...  Please help me!  Thanx!  L8r!  GD

That means DOS had a read error when it tried to access the drive.
Could be DOS couldn't find its IO.SYS or MSDOS.SYS file, or
you could have a real problem and your format or FAT is messed up.
Check to see that DOS' system files are in the path when you run it.

If your testing a floppy, did you mount it first?
DoubleSpace's automount feature can be defaulted off,
or DBLSPACE.BIN might not be in the path.

If your testing a hard drive, did you try running CHKDSK on the
compressed volume's drive letter?  It can only check physical drives.

To check a compressed volume use SCANDISK and give it the physical drive
letter and the volume name, i.e. SCANDISK C:\DBLSPACE.000

If DOS can find all its files, SCANDISK is your best shot at fixing it.

If you had a head crash and the FAT's damaged or the heads are out of
alignment you'll have to try to reformat it or even repartition it.