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A Real-Space Designation for Using Real Addresses along with Virtual Addresses Disclosure Number: IPCOM000013749D
Original Publication Date: 2002-Dec-11
Included in the Prior Art Database: 2003-Jun-18

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In z/Architecture, virtual addresses may be translated to real addresses, for addressing main storage, by means of dynamic address translation (DAT). Whether DAT is off or on is controlled by a bit in the program status word (PSW). DAT uses from zero to three levels of region table, a segment table, and a page table. A DAT-table structure is anchored by an address-space-control element (ASCE). An ASCE may be a region-table designation (RTD), segment-table designation (STD), or, as provided by this invention, a real-space designation (RSD). An RSD specifies that translation is to be performed by transforming a virtual address to an identical real address without the use of DAT tables. An RSD provides a performance advantage in a program that must frequently alternate between accessing virtual and accessing real locations, as in the case of a real-storage manager that manipulates DAT tables. The advantage derives from that the program can keep DAT on instead of frequently turning DAT off and then back on; turning DAT off or on is a time consuming operation because it drains the pipeline of the CPU. It also requires that the program be at the same location in both virtual and real storage. An ASCE may be in a control register or, in the access-register mode, in an ASN-second-table entry (ASTE). In the access-register mode, an instruction B field is used both to form the virtual address of a storage operand and to designate an access register. An access-list-entry token (ALET) in the access register designates an access-list entry, which in turn designates an ASTE. The ASCE in the ASTE then is used to translate the virtual address. Various authorization mechanisms are used to allow the accessing of the ASTE. An RSD for use in alternatively accessing both virtual and real locations should be in an ASTE and used in the access-register mode. An RSD has the following format: Real-Space Token Origin G|P|S|X|R| 0 52 54 54 63