Suppose I've installed Linux on my flash drive. Why do I need something like the casper loop file to make saving persistent? So files are being erased? Isn't the flash drive the same as actual hard disk drive? I'm a Linux noob so be patient.
Or it is because Linux on a flash drive is actually like live CD on a flash drive? Can it be installed just like it is installed on a hard disk drive?
Casper is basically a storage container for Linux systems which downloads programs/drivers/settings anything that is software based is saved in. The files that are not in the casper drive are either the live cd (which would be on a USB drive in this case) and user-created files such as Open Office documents, pictures, and videos. Don't use up the free space on your USB drive with casper or you won't have room to save documents on the drive.
You can install Linux onto your flash drive which in turn wouldn't need a casper persistent storage because of how it runs, but it renders the USB drive as only usable on the pc that it was installed with.
That's what casper provides because a live USB drive can be used on many pcs with the same hardware configuration as the version you downloaded, and casper brings your programs and settings with you.