Patent ID: 7464249

Claim:
A method for mapping address space to enable access of said address space by an operating system including upgraded and legacy portions, said upgraded portion operating in a first address mode capable of accessing all of said address space and said legacy portion operating in a second address mode capable of accessing only a subset of said address space, comprising: providing real storage including first and second address spaces, said second address space being smaller than and contained within said first address space; providing virtual storage; providing within said virtual storage a system execution space (SXS); providing within said system execution space a system execution area (SXA) having a size equal to or less than said second address space, both SXS and SXA being subsets of said real storage; providing within said system execution area said operating system comprising a control program including first and second portions, said first portion being an upgraded portion capable of addressing said first address space and said system execution space, said second portion being a legacy portion capable of addressing any address within real storage aggregating to less than said first address space; providing within said system execution area at least one alias page; responsive to a control program request for a first page in said virtual storage, dynamically assigning a first frame in said real storage corresponding to said page; responsive to a request from said second portion of said control program for said first page, dynamically assigning an alias page in said system execution area, and assigning said alias page to said first frame, thereby also mapping said first frame to said first page in said virtual storage, without moving said first page into a frame in real storage directly addressable by said legacy portion of said operating system; responsive to a first request from said first portion of said control program to pin said first page, pinning said first page; and responsive to a second request from said second portion of said control program to pin said first page, assigning an alias page for pinning said first page on behalf of said second request without moving said first page thereby providing concurrent access to both said system execution area by said legacy portion of the operating system and all of real storage by said upgraded portion of said operating system.