Multiple versions on one box

Hi

Could someone help me with the below questions.

We have multiple MaxDB databases running on one box for EC and BW. There is a requirement to upgrade the BW database software, to do this do I have to upgrade the other databases on the box? Though my OS is Linux, I would also like to know the possibilities in windows environement.

If we can have multiple versions of databases on one box, are there any known problems. If the database version are different, how does the common services or executables work (eg:- I understand that there is only on XSERVER per box) and which folders are updated (is it only "database_dependent_path" or "independent_program_path" as well)?

Please advise

Thanks