This information describes some areas you might need to consider if migrating programs from IBM COBOL for AIX Version 2 or Version 3 to IBM COBOL for AIX Version 4.
related references
Object code
Data size limits
Initialization of EXTERNAL data
STL and SdU files that are larger than 2 GB
SFS files
File identifiers
Object-oriented syntax, and Java 5 or Java 6
XML generation
Migration of 32-bit applications to 64-bit mode
Reserved words (COBOL for AIX Language Reference)