
Glossary of Terms and Abbreviations
Glossary-7
Memory-mapped accesses
. Accesses whose addresses use the segmented or
block address translation mechanisms provided by the MMU and
that occur externally with the bus protocol defined for memory.
Memory coherency
.
Refers to memory agreement between caches and
system memory (for example, MESI cache coherency).
Memory consistency
.
Refers to levels of memory with respect to a single
processor and system memory (for example, on-chip cache,
secondary cache, and system memory).
Memory management unit
. The functional unit that is capable of translating
an
effective
(logical)
address
to a physical address, providing
protection mechanisms, and defining caching methods.
MESI (modified/exclusive/shared/invalid)
.
Cache coherency
protocol used
to manage caches on different devices that share a memory system.
Note that the PowerPC architecture does not specify the
implementation of a MESI protocol to ensure cache coherency.
Modified
state
. When a cache block is in the modified state, it has been
modified by the processor since it was copied from memory.
See
MESI.
Multiprocessing
. The capability of software, especially operating systems,
to support execution on more than one processor at the same time.
Most-significant bit (msb)
. The highest-order bit in an address, registers,
data element, or instruction encoding.
Most-significant byte (MSB)
. The highest-order byte in an address,
registers, data element, or instruction encoding.
OEA (operating environment architecture)
. The level of the architecture
that describes PowerPC memory management model, supervisor-
level registers, synchronization requirements, and the exception
model. It also defines the time-base feature from a supervisor-level
perspective. Implementations that conform to the PowerPC OEA
also conform to the PowerPC UISA and VEA.
Optional
. A feature, such as an instruction, a register, or an exception, that is
defined by the PowerPC architecture but not required to be
implemented.
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