Never mind Alias - it's a Linux Troll who gives ill advise intentionally to
cause pain to Windows users.
Now I don't know how to fixate Drive Letter as it changes dynamiclaly to
reflect currently installed drives, so if you don't change the number of
drives the same letter should remain for your portable, if you dynamically
attach/detach, the letters will be assigned just in alphabetical order
except for A: & B: which were historically reserved for floppies (if you're
too young you won't udnerstand what I mean by floppies), and C: for primary
harddisk, all else is quite random.
But why do you bother???
Most people NAME their diskdrives, yes I wish I could have the same letter
for the same drive besides A, B, C which are fixated alreadde, but we use
names.
E.g. I named my C:\ as "MAIN FOLDER", external USB as "MINIFOLDER1",
external USB another as "MINIFOLDER2", USBflashstick as "SOLIDFOLDER"
And names don't change sinec it's written intto the drive.
But again i am not too deeply knowledged on this, as I don't care for having
the same letter assigned, so PLEASE:
WAIT FOR MORE RESPONSES.
Don't listen to Alias or DanS or whatever name he chooses next, it's a known
pest on Windows forums who comes here to promote hobbyist Operating System
known as Linux.