pmedia=cd will generally work for any install, but it is not setup to correctly run the boot process for every type install.
So not best way to boot if not booting from a CD/DVD install.
It does first boot in pupmode 5 and change to pupmode 12 after booting using a save.
So this save operation will work for any type install, but may not be best for type drive device it is on.
During the boot process it is doing stuff only needed for a CD/DVD install.
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The first time you boot.
Pmendia=cd is telling the boot process to boot as needed for an install on a CD/DVD.
How to find the files and a save if there is one to use.
It is used in the boot loaders provided in the Puppy version ISO, because the ISO is setup to provide all that is needed for a live install to a CD/DVD.
pmedia=cd causes the boot process to boot in pupmode 5.
This is running with no save and using a save ramdisk (part of memory) to function as the save.
All changes go into the save ramdisk.
On first shutdown and making a save file or folder.
Contents of the save ramdisk are put in the save you make.
Now when it boots using the save it is running in pupmode 12.
No save ram disk and directly writes to the save with any changes.
pmedia=cd also controls how the boot up process looks for the save file/folder.
Because the save could be on any drive any partition.
It is not going to be on the CD.
So searching for the save has been an issue with frugal installs, because they are not on a CD/DVD.
It searches too much.
Note:
A CD/DVD burned open can put a save on the CD/DVD at it will boot in pupmode 77
Still use a save ramdisk and update the save by writing it to the CD/DVD on shutdown.
pmedia=usbflash or pmedia=ataflash (any with flash) 1st boots the same way into pupmode 5. (applies to SSD drives)
Uses a save ramdisk and will always use a save ramdisk.
This is setup for installs on a USB flash drive to limit writes to the drive. Any flash type drives.
After making the save file/folder and booting using it.
It runs in pupmode13.
Changes first go into the save ramdisk and then go into the actual save file/folder when told to update the save.
When it boots and looks for the save.
It looks on the location the Puppy files are and usually will find the save there.
So it does not search all possible drives.
(however, in newest Puppies this may now allow putting the save on another drive, to be able to remove the USB after boot up)
pmedia=atahd or pmedia=usbhd sets up the boot process to boot for a drive that how many writes to is not a issue.
1st boots into pupmode 5 using a save ramdisk.
1st shutdown making a save.
2nd boot using the save is running in pupmode 12.
Writing to the save is directly as anything changes.
Yes you could make the pmedia= anything you want.
But making it correct for the type of drive booting from is making the boot process work correct for the type of drive.
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Using pmedia=usbflash for any drive installed on.
Is a trick way to run in pupmode 13 and have the features of this mode.
But not for booting from an install on a CD/DVD