Address Space - in the MVS operating system this is an area of memory that contains a system task, user program, or TSO user. It consists of 16Mb of virtual storage. It is broken into system, private and common areas with unique segment and page tables for it's private area. It shares page, segment tables for the common area with all other address spaces. The entire core memory of the computer is divided into segments, 256 65K each, and further into pages, 16 at 4K each.
From: BitSavers IBM Section