You will find differences in the way DB2 server is referred to and accessed on these two platforms. DB2 server is called a subsystem in z/OS and an instance in LUW. DB2 runs its tasks under a set of address spaces in z/OS system (discussed in Memory structures), as a process in Linux and UNIX operating systems, and as a service (unless you started with /D option) in Windows. Each DB2 z/OS server is identified by a four character subsystem identifier (SSID), and each DB2 LUW server is identified by an instance name that takes effect through the DB2INSTANCE environment variable.
What does the term database mean in each platform? A database in DB2 LUW has its own memory region, processes, and recovery logs, while a database in DB2 z/OS is a logical collection of several table spaces and index spaces with very few parameters defined as default for all objects created under it. While each database in DB2 LUW holds its exclusive catalog tables, it is every DB2 subsystem that holds catalog tables.
A DSNDB06 database in DB2 z/OS subsystem, and a SYSCATSPACE table space in DB2 LUW will hold all the DB2 catalog tables.
In non-data sharing DB2 z/OS, DSNDB07 is the work-file database. Table spaces that you create in DSNDB07 will be used as storage for processing SQL joins and sorts as well as for temporary tables. In DB2 LUW, a default system temporary table space called TEMPSPACE1 will be available for such DB2 DBM requirements as sorts or joins. You should create one or more USER temporary table spaces for storing data of temporary tables.
When you do not specify the database name while creating a table space or table in DB2 z/OS, DSNDB04 is the default user database for the created object. If you create a table without specifying a table space, DB2 will create an implicit table space for you. In DB2 LUW, assuming you have not created any user table spaces yet, USERSPACE1 will hold the tables you create without specifying the table space explicitly.
DB2 z/OS uses several information required for normal operation in a special database, DSNDB01. Boot Strap Dataset (BSDS) is a z/OS VSAM dataset that will contain some critical information regarding DB2 recovery log dataset names, DB2 checkpoints and DB2 location details. On the other hand, DB2 LUW database stores several information required for normal operation across several operating system files under local database directory.