Like pupmode=5 and pupmode=77, the RW layer is a directory in a tmpfs in RAM, and Puppy runs completely in RAM.
And also a little bit like pupmode=77;
On shutdown, the contents of the RW directory are written to an archive file, with some exclusions.
On boot, the empty RW directory in RAM is populated with the contents of the archive file.
pupmode=66 is not very efficient if the save layer is heavily used, e.g. by installing lots of .pet's.
But this is meant for only a "simple" 'StickPup' style installation, (all on a single "vfat" partition).
For "heavy" use an 'f2StickPup' style installation would be better, (save folder on a Linux partition).
Why?
It's simple, it can easily and safely be setup automatically on any filesystem,
it only uses as much disk space as the data requires, and the data is compressed when saved.
So it can be used as an "AUTOSAVE" mechanism on any non-Linux filesystem, e.g. on a Puppy installed with StickPup.
In the current implementation, the archive file is a ".tar.gz" file.
It is only activated if the save location is on a "vfat" partition, and if a file named "AUTOSAVE" is present in the save location.
'StickPup' v24 writes an "AUTOSAVE" file, so that on first-shutdown the only dialog is "SAVE/No",
provided the target Puppy contains the latest patches from the "init-experiment" branch of woof-ce.
You can try it by patching the currrent "UPupGG+D" or "eslacko64":
1. Download "FrugalPup v24"
2. Install 'UPupGG+D-20.10+5.iso' or 'eslacko64-6.9.9.12.iso' with 'StickPup v24'
3. Download 'upupgg+d_20.10_pm66.tar.xz' or 'eslacko64_6.9.9.12_pm66.tar.xz' from https://www.mediafire.com/folder/j2u10wl713fky/pm66.
4. Extract the contents of the ".tar.xz" file into the Puppy install directory on the usb stick, replacing 'initrd.gz' and adding a 'ydrv_...sfs' file.
5. Boot the usb stick.
6. On first-shutdown, select "SAVE", there should be no more dialogs, and the session should be saved to a ".tar.gz" file.
7. On next boot of the usb stick, changes made during the first-boot should be restored, and '/etc/rc.d/PUPSTATE' should contain "PUPMODE=66".
gyro