dbdkdoc.txt
Describes features that are not covered in the manuals or that have been modified since publication.
dbdkrel.txt
Describes feature differences from earlier versions of Informix products and how these differences might affect current products. This file also contains information about any known problems and their workarounds.
These files are located in the %INFORMIXDIR%\release directory under the subdirectory for your locale. Please examine these files because they contain vital information about application and performance issues.