State or Function STE is attached by means
of PSTO (applies only to STE in storage) STE is attached by means
of SSTO (applies only to STE in storage) STE in storage is usable
for a particular instance
of implicit translation STE can be placed in TLB STE in TLB is usable STE in TLB is usable for
a particular instance of
implicit translation PTE is attached (applies
only to PTE in storage) PTE in storage is usable
for a particular instance
of implicit translation Conditions to Be Met • DAT on • No early PSW exception* • TF valid • STE in segment table defined by PSTO in CR1 • STE selectable by a 24-bit ad­
dress • OAT on • No early PSW exception • TF valid • STE in segment table defined by SSTO in CR7 • STE selectable by a 24-bit ad­
dress • PSW bit 16 one or bit 5 of CRO one • STE in segment table defined and
attached by STO being used for
the translation • STE selected by SX • STE attached • STE I bit zero • No TS • OAT on • No early PSW exception* • TF matches • STE selectable by an STO: - C bit one7 or
- STO matches PST07 or
- STO matches SST0 7 and either PSW bit 16 one or bit 5 of CRO one • OAT on • No early PSW exception* • TF matches • STE selected by STO being used
for the translation:
- STO matches7 or
- C bit one • SX matches • PTE in page table defined by
usable STE in the TLB7 or de­
fined by an STE that can be
placed in the TLB • PTE attached by means of STE
being used for the translation • PTE selected by PX Summary of OAT Entries (Part 1 of 2) Chapter 3. storage 3-35

State or Function Conditions to Be Met
PTE can be placed in TlB • PTE attached • PTE I bit zero • No TS PTE in TlB is usable • TF matches • PTE selectable by a usable STE in the TLB or by an STE that
can be placed in the TlB:
- PTO matches and - PX within PTl • TF matches PTE in TlB is usable for
a particular instance of
implicit translation • PTE selected by STE being used
for the translation:
- PTO matches and
- PX within PTl • PX matches
Explanation: * C bit
I bit PSTD PSTO PTE PTl PTO PX SSTD SSTO STD STE STO SX Models which do not have DAS installed do not
necessarily comply with the condition. Common-segment bit in STE. Invalid bit in table entry.
Primary segment-table designation.
Primary segment-table origin. Page-table entry.
Page-table length.
Page-table origin. Page index. Secondary segment-table designation. Secondary segment-table orlgln. Segment-table designation. Segment-table entry. Segment-table origin. Segment index.
TF TS Translation format (control register 0, bits 8-12).
Translation-specification exception. The condition
"No TS" means that attempted use of the associated
OAT-table entry would not cause a translation­
specification exception. Summary of OAT Entries (Part 2 of 2)
Modification of Translation Tables
When an attached and invalid table entry
;s made valid and no usable entry for
the associated virtual address is in the TlB, the change takes effect no later
than the end of the current unit of
operation. Similarly, when an unat­
tached and valid table entry is made
attached and no usable entry for the
associated virtual address is in the
TlB, the change takes effect no later
than the end of the current unit of
operation.
When a valid and attached table entry is
changed, and when, before the TlB is
cleared of entries which qualify for
substitution for that entry, an attempt
is made to refer to storage by using a
virtual address requiring that entry for
translation, unpredictable results may
occur, to the following extent. The use
3-36 System/370 Principles of Operation
of the new value may begin between
instructions or during the execution of
an instruction, including the instruc­
tion that caused the change. Moreover,
until the TlB is cleared of entries
which qualify for substitution for that
entry, the TLB may contain both the old
and the new values, and it is unpredict­
able whether the old or new value is
selected for a particular access. If
both old and new values of a segment­ table entry are present in the TLB, a
page-table entry may be fetched by using
one value and placed in the TlB associ­
ated with the other value. If the new
value of the entry is a value which
would cause an exception, the exception
mayor may not cause an interruption to
occur. If an interruption does occur,
the result fields of the instruction may
be changed even though the exception
would normally cause suppression or
nullification.