Alek wrote:
With a known good HD plugged in to one and then to a USB port, it shows
up on my computer as O:

It shows up as having 5 partitions, etc.

When I plug it into the other holder and plug that one into the USB port
that I had just been using, shouldn't it show up as O: also?

There's a tool to increase the number
of variables :-) Drive Letter Manager (DLM)
can add some certainty to assignments.

https://www.uwe-sieber.de/usbdlm_e.html

I don't worry about letters all that much,
and so far haven't managed to place a dependency
on what letter a USB is assigned. As a consequence,
I don't use DLM.

As a corollary, I have to be *very careful*
in Disk Management. Any time I issue commands,
I check, check, and recheck that drive letter.
I also no longer copy commands in a hurry
into Command Prompt. I prepare a command
in Notepad, copy the string, *Paste* it
back into Notepad to verify the paste buffer
contains what I think it contains. Only
then, do I go back to the Command Prompt
and paste the string into there too. After
which, if I'm happy with the command entered,
I hit the Enter key. These extra steps were
after having a "little accident" that deleted
1GB of files before I could stop it.

Paul