The DB2 Universal Database family consists of many different platforms that can coexist in a distributed environment:
z/OS or OS/390
This offering is the largest of the DB2 family, often used as an enterprise server handling some of the largest applications in the world. The System/390 is IBM's largest hardware platform.
This offering is often used to build e-business applications and to support large departmental applications. It offers the most connectivity options and can share data with third-party databases and DB2 on heterogeneous platforms.
This offering is often used in smaller departmental applications or for applications that do not need access to remote databases on the OS/400, ...