Libraries and objects are not everything. The i5 also uses DASD to store the system microcode, PTFs applied temporarily, system values, and all the QTEMP libraries. None of these items is stored in any library.
The system also occasionally places objects (such as files or programs) outside of any library. This is an abnormal situation, but it happens now and then, and is corrected by running the Reclaim Storage (RCLSTG) command.
The i5 also supports other file systems in addition to the library file system. Most of these systems are like the directory-based file systems of personal computers and Unix machines. The library file system and the other file systems are known collectively as the Integrated File System (IFS).
The Work with System Status (WRKSYSSTS) command displays the total amount of DASD in use. If you add up the sizes of all the objects in all the libraries, plus the sizes of the libraries themselves, you will not obtain the number shown by WRKSYSSTS. The difference is equal to the sum of all the items that are outside of libraries.