Version - chronology

Here we see each version/release of DB2 in its thirty year history, along with its date of general availability. The other two columns, EoM and EoS, are end-of-marketing and end-of-service dates. An EoM date means that IBM will no longer sell that version of DB2 as of that date; EoS means that IBM will no longer officially support that version of DB2 as of that date. 

Version	GA	EoM	EoS		SKIP	Code
1.1	1985-04-02			No Skip Level		ASCII/EBCID
1.2	1986-03-07			No Skip Level		ASCII/EBCID
1.3	1987-06-26			No Skip Level		ASCII/EBCID
2.1	1988-09-23			No Skip Level		ASCII/EBCID
2.2	1989-09-22			No Skip Level		ASCII/EBCID
2.3	1991-10-25			No Skip Level		ASCII/EBCID
3	1993-12-17	1999-11-30		SKIP Level		ASCII/EBCID
4	1995-10-30	2000-12-01		SKIP Level		ASCII/EBCID
5	1997-06-27	2001-12-31	2002-12-31	SKIP Level		ASCII/EBCID
6	1999-06-15	2002-06-30	2005-06-30	SKIP Level		ASCII/EBCID
7	2001-03-30	2007-03-05	2008-03-30	SKIP Level		ASCII/EBCID
8	2004-03-26	2009-09-08	2012-04-30	SKIP Level Mode level		UNICODE/ASCII/EBCID
9	2007-03-06	2012-12-10	2014-06-27	SKIP Level Mode level		UNICODE/ASCII/EBCID
10	2010-10-22	2015-07-06	2017-09-30	SKIP Level Mode level		UNICODE/ASCII/EBCID
11	2013-10-25			SKIP Level Mode level		UNICODE/ASCII/EBCID
12				No SKIP / No Mode		UNICODE/ASCII/EBCID

From DB2 V8 unicode has been introduced to avoid ASCII/EBCID . Also Mode level in upgradation introduced.

CM      -           Compatabilty Mode

ENFM  -           Enable new function mode

NFM    -           New Function Mode

DB2V9 catmaint can run on ENFM .We can fall back from ENFM to CM

V10 -> V11 –> V12 allowed

V10 -> V12 Not allowed