Domino 653 on RHLinux

Hi , I need to know on Domino server 653 running on RHEL why we get so many processes when we use the top command .We have 2 GB RAM and using the free command most of the memory is in used state even when thee are 3 users .Also in the Notes User under Server tab in Domino Admin client I find for a single user when connected multiple instances /session.Why is this so ?Is it normal ,kindly advise as I am new to Domino world.

One person suggested me to Upgrade to Domino 7 .How good is the new release in terms of performance on both Windows and Unix (all flavors)?

Merry Christmas and a Happy New Year 2006 to all of you.

Regards,

TS