[Borgbackup] Newbie questions

[Joseph Hesse]

Hello

I have two questions that I don't seem able to find in the docs.

What is the difference between running Borg backup with the repo on an 
external hard drive vs the repo on a server?  I thought in both cases 
Borg runs on the local machine, does its work and updates the repo, 
whether the repo resides on a drive or a server.  The reason I ask is 
that servers hosting Borg backup have Borg software running on them and 
I don't understand what the server specific Borg software does.

Is there a problem with two or more local machines using the same repo?

I thank you in advance.

Joe