System for designating real main storage addresses in instructions while dynamic address translation is on

An apparatus for addressing a required central storage location in a system with central storage having central storage addresses and a dynamic address translation (DAT) mechanism for translating a specified virtual storage address into an associated central storage address, said apparatus comprising:

• means for storing a DAT indicator having a first value to indicate that DAT is enabled in the system, and a second value to indicate that DAT is disabled in the system;
• an access register mechanism comprising a plurality of registers storing address data, usable by said DAT mechanism in performing said translating when the system is executing an instruction while in access register (AR) mode with DAT enabled;
• and
• translation means coupled to said DAT indicator for utilizing an address specified by an instruction being executed in said AR mode for referencing a predetermined central storage address directly using said address as a central storage address while said DAT indicator has said first value and for referencing a predetermined central storage address indirectly through said DAT mechanism using said address as a virtual address while said DAT indicator has said second value.