Hi
For newbies like me having very old laptops like mine.
Booting from a 1 or 2To usb_hdd is impossible but it becomes possible in 2 ways to work "directly" on such a disk.
1- First way usually known via "bootfrom=*.iso" after having copied the "iso" and
having booted with a "knoppix_7.*" disk (CD,DVD, or light flash up to 500Go).
This method DOES NOT SAVE CHANGES DONE.

2- The 2nd Method which SAVE CHANGES
a- On the root of the "high Disk" copy the entire folder of aKnoppix installed flash or usb_disk.
b- Boot with the choosen installed flash or usb
(without plugging the "high one" ! Otherwise one cannot even boot!...a Bios
problem).
c- Once having the 1st screen (ready for cheatcodes) type the command (for
example):
bootfrom=/dev/sdd1/
d- Plug the" high disk" and wait a moment for complete mounting it.
e- the touch "ENTER"
f- UNplug the bootdisk just after complete "decompressing kernels"
( just when the second screen appears with messages like " ...Elf..." )
g- Let (PATIENTLY!) the system try 20 TIMES to "continue the complete booting.
h- After these "20 trying" the system WILL CONTINUE with the "knoppix.img"
contained in the folder "KNOPPIX" on the root of the new high_usb_hdd.
Remarks:
a- This method works like the normally well installed flash or ligth usb_hdd
b- It looks like the "boot_from_ISO" with a shorter cheatcode
c- Its 3rd interest is the SAVING CHANGES like a well installed light flash disk.
d- Registring heavy files becomes very DIRECT on the root via the "KNOPPIX_link"
on the Desktop ( the root="mnt-system" as "usually"...!).
Perhaps all of this is "easy" for very acquainted readers.
Perhaps useful for old laptops and newbies.
Bye
knp