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by the MMU whenever the page is accessed for a read or write
operation. The changed bit is set when the page is stored into. See
Changed bit and Referenced bit.
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Page fault. A page fault is a condition that occurs when the processor
attempts to access a memory location that does not reside within a
page not currently resident in physical memory. On PowerPC
processors, a page fault exception condition occurs when a
matching, valid page table entry (PTE[V] = 1) cannot be located.
Page table. A table in memory is comprised of page table entries, or PTEs.
It is further organized into eight PTEs per PTEG (page table entry
group). The number of PTEGs in the page table depends on the size
of the page table (as speciÞed in the SDR1 register).
Page table entry (PTE). Data structures containing information used to
translate effective address to physical address on a 4-Kbyte page
basis. A PTE consists of 8 bytes of information in a 32-bit processor
and 16 bytes of information in a 64-bit processor.
Physical memory. The actual memory that can be accessed through the
systemÕs memory bus.
Pipelining. A technique that breaks operations, such as instruction
processing or bus transactions, into smaller distinct stages or tenures
(respectively) so that a subsequent operation can begin before the
previous one has completed.
Precise exceptions. A category of exception for which the pipeline can be
stopped so instructions that preceded the faulting instruction can
complete, and subsequent instructions can be ßushed and
redispatched after exception handling has completed. See Imprecise
exceptions.
Primary opcode. The most-signiÞcant 6 bits (bits 0Ð5) of the instruction
encoding that identiÞes the type of instruction.
Program order. The order of instructions in an executing program. More
speciÞcally, this term is used to refer to the original order in which
program instructions are fetched into the instruction queue from the
cache
Protection boundary. A boundary between protection domains.
Protection domain. A protection domain is a segment, a virtual page, a BAT
area, or a range of unmapped effective addresses. It is deÞned only
when the appropriate relocate bit in the MSR (IR or DR) is 1.
Glossary of Terms and Abbreviations
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