External Dummy Sections, also called pseudoregisters, are varying sized units of program storage that do not occupy space in the load module or program object. External Dummy Sections are defined by compilers, or by the assembler using the DXD instruction, and are shared among all sections in the module in the same way that common areas are shared. The attributes of the single, mapped area represents the cumulative length obtained by assigning each pseudoregister's longest length and most restrictive alignment from all its definitions. Virtual storage for the pseudoregister(s) is not provided in the program module, but is instead obtained during execution, using the aggregate length of all pseudoregisters provided by the linker. The concatenation of all uniquely named pseudoregisters is called the pseudoregister vector.