There’s a good article on http://www.ibm.com/developerworks/data/library/techarticle/dm-0807kharche/ outlining the DB2 9.5 process model.
1) New memory model
2) Increased automatic configurations . According to the article , less is required of the DBA. Based on my experience since DB2 9.5 – there’s some truth in this point. The focus is now more on architecture and DB2 performance tuning. Designing for scaling is a critcal part of designing the database server system
3) Process model is the same for : Linux,Unix and Windows
4) Context Switching between threads is quicker than process switching. Less resource is required . One process has multiple threads -Author: Jack Vamvas(http://www.dba-db2.com)