Each address-space translation mode translates virtual addresses corresponding to that address space. For
example, primary address-space mode translates virtual addresses from the primary address space, and home
address space mode translates virtual addresses belonging to the home address space.
Each address space has an associated Address Space Control Element (ASCE). For primary address
translation mode, the Primary Address Space Control Element (PASCE) is obtained from the CR1. For
secondary address translation mode, the Secondary Address Space Control Element (SASCE) is obtained
from the CR7. For home address translation mode, the Home Address Space Control Element (HASCE) is
obtained from the CR13. In access-register translation mode, the Access List Entry Token (ALET) in the
access register is checked. If it is the special ALET 0, PASCE is used. If it is the special ALET 1, SASCE is
used. Otherwise, the ASCE found in the Address Space Number (ASN) table is used. SLES does not use the
translation by the Address Space Number feature of the z/Architecture.
After the appropriate ASCE is selected, the translation process is the same for all of the four address
translation modes. The ASCE of an address space contains the region table, for 64-bit addresses, or the
segment table, for 31-bit addresses, origin. DAT uses that table-origin address to translate a virtual address to
a real address, as illustrated below.
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