PostGreSql database features questions

Hi:

I'm very new to PostGreSql database and actually looking to evaluate for
one of our project needs.  Below please find some questions.  I'm hoping
if I can get some insight into these questions.

Thanks.

Ish...

1)  Does PostGreSql allows for multiple databases to be open at the same
time?

2) Does PostGreSql have the ability to tag a Database/Table to be a
persistent or non-persistent database/table?  By this question I mean,
that I may need to have a table that I don't want to be saved to the
hard disk/ flash file system and only want to keep it in memory and
other tables/database I may want to save to hard disk or flash.  Does
PostGreSql allow for that?