Motorola MPC860 PowerQUICC, User Manual, Page: 1081 / 1106

MOTOROLA Glossary of Terms and Abbreviations Glossary--7
Most-signiÞcant byte (MSB). The highest-order byte in an address,
registers, data element, or instruction encoding.
No-op. No-operation. A single-cycle operation that does not affect registers
or generate bus activity.
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 deÞnes 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
deÞned by the PowerPC architecture but not required to be
implemented.
Out-of-order. An aspect of an operation that allows it to be performed ahead
of one that may have preceded it in the sequential model, for
example, speculative operations. An operation is said to be
performed out-of-order if, at the time that it is performed, it is not
known to be required by the sequential execution model. See
In-order.
Out-of-order execution. A technique that allows instructions to be issued
and completed in an order that differs from their sequence in the
instruction stream.
Overßow. An error condition that occurs during arithmetic operations when
the result cannot be stored accurately in the destination register(s).
For example, if two 32-bit numbers are multiplied, the result may not
be representable in 32 bits.
Pace control. Controls the rate of the data ßow between a master and slave.
Page. A region in memory. The OEA deÞnes a page as a 4-Kbyte area of
memory, aligned on a 4-Kbyte boundary.
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.
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