Are u looking for difference between directories and catalog tables?
Catalog tables are set of tables that is maintained by DB2 and contains the information of all the objects that have been defined in the DB2 subsystem.
Eg -tables,views stored proc,routines,dbrms,plans,packages database,TS etc...
Whenever u alter/define any object corresponding rows are inserted/updated/deleted from the respective catalog tables.
doing runstats with update option updates the catalog tables accordingly and allowing the DB2 optimizer to get the most optimized access path.
Most of the catalog tables are stored in DSNDB06
As far as directories are concerned ..they are stored in 5 TS in DSNDB01(System Database).
The directoried are used during normal operation of DB2 and it is not accessible by sql queries.
they are like SPT01,SCT01,SYSLGRNX,SYSUT1 ...
SPT01 stores infoemation abt access path for a package in internal form of SQL.
SCT01-stores info abt access path for a plan in internal form of SQL
SYSUT1- contains corresponding entries of the utilitiy that is running