Abstract: A disk operating system converts virtual storage space locations of one or more processes into real disk or core memory storage space locations of a computer system. Real and virtual storage space are divided into equal sized pages. Real storage pages are grouped into variable sized segments and a separate segment page table is provided for each real storage segment, each entry therein characterizing the nature and location of a page. A separate process map list is provided for each process, each entry therein mapping an area of contiguous virtual storage pages onto a segment page table. Before a process executes a program, the operating system uses the associated process map list, along with the segment page tables mapped by the list, to create a process page table which directly maps virtual storage pages of a process into real storage pages.