GMC 2007 Envoy Denali Owner's Manual page 272

The player is able to read and play a maximum
of 50 folders, 50 playlists, 10 sessions, and
255 files. Long file names, folder names, or playlist
names can use more disc memory space than
necessary. To conserve space on the disc,
minimize the length of the file, folder, or playlist
names. You can also play an MP3 CD that
was recorded using no file folders. The system
can support up to 11 folders in depth, though, keep
the depth of the folders to a minimum in order
to keep down the complexity and confusion
in trying to locate a particular folder during
playback. If a CD contains more than the
maximum of 50 folders, 50 playlists, 10 sessions,
and 255 files the player lets you access and
navigate up to the maximum, but all items over
the maximum are ignored.
Root Directory
The root directory is treated as a folder. If the root
directory has compressed audio files, the directory
displays as F1 ROOT. All files contained directly
under the root directory are accessed prior to any
root directory folders. However, playlists (Px) are
always accessed before root folders or files.
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Empty Directory or Folder
If a root directory or a folder exists somewhere in
the file structure that contains only
folders/subfolders and no compressed files directly
beneath them, the player advances to the next
folder in the file structure that contains compressed
audio files. The empty folder does not display.
No Folder
When the CD contains only compressed files, the
files are located under the root folder. The next
and previous folder functions do not function on a
CD that was recorded without folders or playlists.
When displaying the name of the folder the
radio displays ROOT.
When the CD contains only playlists and
compressed audio files, but no folders, all files are
located under the root folder. The folder down
and the folder up buttons search playlists (Px) first
and then goes to the root folder. When the
radio displays the name of the folder the radio
displays ROOT.