Real storage Address
PFRA PFRA
without Extended with Extended
Real Addressing Real Addressing Byte IndexSize Bit Bit Bit
of PositionsNo. Positions No. Positions No. Page in Page-of in Page-of in Virtual of
(Bytes) Table Entry Bits Table Entry Bits Address Bits
2K0-12 13 0-12 13 21-31 11
4K0-11 12 13, 14, 0-11 14 20-31 12
Segment Number Max Segm Tbl
Size Index of Segment-
of Field Address-Usable Table
Segment Size able Size Length Increment
(Bytes) (Bits) Segments (Bytes) Code (Bytes)
64K 8 256 1,024 15 64
1M 4 16 640 64
Page Max Page Tbl
Size of Index Number
Field of Pages
Segment PageSize in Size
(Bytes) (Bytes) (Bits) Segment (Bytes)
64K 2K 5 32 64
64K 4K 4 16 32
1M 2K 9 5121,024 1M 4K 8 256 512 TRANSLATION PROCESS This section describes the translation
process as itis performed implicitly
before a virtual addressis used to
access main storage. The process of
translating the operand address ofLOAD REAL ADDRESS and TEST PROTECTION is the same, except that segment-translation
and page-translation exceptions do not
occur; such situationsare instead indi cated in the condition code.
Translation ofthe operand address of LOAD REAL ADDRESS also differs in that
the CPU may bein the real mode and the
translation-lookaside buffer is not
used.
Translation of a virtual address is
performed by means of a segment table
and a page table both of whichreside in
real storage. It is controlled by the
OAT-mode bit in thePSW and by the
translation parameters in control regis
ters0 and 1. When DAS is installed,
translation is also controlled by the
address-space-control bit in thePSW, and the translation parameters also
include control register 7.Page- Usable Table
Length Increment
Code (Bytes)
15 4
15 2
15 64
15 32
Effective Segment-Table Designation
The segment-table designation used for a
particular address translation is called
the effective segment-table designation.
Accordingly, when a primary virtual
address is translated, control register
1 is used as the effective segment-table
designation, and when a secondary virtu
al address is translated, control
register 7 is used as the effective
segment-table designation. Without DAS,
the term "effective segment-table desig
nation" is synonymous with "primary
segment-table designation."
The segment-index portion of the virtual
address is used to select an entry from
the segment table, the starting address
and length of which are specified by the
effective segment-table designation.
This entry designates the page table to
be used and, if the segment-protection
facility is installed, provides the
segment-protection bit.
The page-index portion of the virtual
address is used to select an entry from
Chapter 3. Storage 3-27
PFRA PFRA
without Extended with Extended
Real Addressing Real Addressing Byte Index
of Positions
(Bytes) Table Entry Bits Table Entry Bits Address Bits
2K
4K
Segment Number Max Segm Tbl
Size Index of Segment-
of Field Address-Usable Table
Segment Size able Size Length Increment
(Bytes) (Bits) Segments (Bytes) Code (Bytes)
64K 8 256 1,024 15 64
1M 4 16 64
Page Max Page Tbl
Size of Index Number
Field of Pages
Segment Page
(Bytes) (Bytes) (Bits) Segment (Bytes)
64K 2K 5 32 64
64K 4K 4 16 32
1M 2K 9 512
process as it
before a virtual address
access main storage. The process of
translating the operand address of
and page-translation exceptions do not
occur; such situations
Translation of
the CPU may be
translation-lookaside buffer is not
used.
Translation of a virtual address is
performed by means of a segment table
and a page table both of which
real storage. It is controlled by the
OAT-mode bit in the
translation parameters in control regis
ters
translation is also controlled by the
address-space-control bit in the
include control register 7.
Length Increment
Code (Bytes)
15 4
15 2
15 64
15 32
Effective Segment-Table Designation
The segment-table designation used for a
particular address translation is called
the effective segment-table designation.
Accordingly, when a primary virtual
address is translated, control register
1 is used as the effective segment-table
designation, and when a secondary virtu
al address is translated, control
register 7 is used as the effective
segment-table designation. Without DAS,
the term "effective segment-table desig
nation" is synonymous with "primary
segment-table designation."
The segment-index portion of the virtual
address is used to select an entry from
the segment table, the starting address
and length of which are specified by the
effective segment-table designation.
This entry designates the page table to
be used and, if the segment-protection
facility is installed, provides the
segment-protection bit.
The page-index portion of the virtual
address is used to select an entry from
Chapter 3. Storage 3-27