This redbook provides information on performance analysis and optimization of three C/C++ applications (a large, a medium, and a small) that had already been ported to OS/390 UNIX System Services (OS/390 UNIX). This redbook will be useful to users, system programmers, application developers and others who are interested in improving the performance of C/C++ applications that have already been ported to OS/390 UNIX. Its intent is to provide a repository of information on improving the performance of already ported C/C++ applications. It does not address application porting to OS/390 UNIX