I think of - Code (base) register: generally old style, when relative addressing is not available - Static Area (base) register: address of your static data (such as literals) Some modules actually have no such data but most do. z/OS macros may assume that you have addressability to such an area, or (fewer, at least when IEABRC(X) is used) they may assume that you have code register addressability. - Dynamic Area (base) register: address of the area that you obtained on module entry for working storage
These show up as, but are not really the same term, as the "base register" of architected instructions. Peter Relson z/OS Core Technology Design
