
Glossary-6
PowerPC Microprocessor Family: The Bus Interface for 32-Bit Microprocessors
Imprecise exception
. A type of
synchronous exception
that is allowed not to
adhere to the precise exception model (
see
Precise exception). The
PowerPC architecture allows only floating-point exceptions to be
handled imprecisely.
Inexact
. Loss of accuracy in an arithmetic operation when the rounded result
differs from the infinitely precise value with unbounded range.
In-order.
An aspect of an operation that adheres to a sequential model. An
operation is said to be performed in-order if, at the time that it is
performed, it is known to be required by the sequential execution
model.
See
Out-of-order.
Instruction queue
. A holding place for instructions fetched from the current
instruction stream.
Interrupt
. An external signal that causes the processor to suspend current
execution and take a predefined exception.
Invalid state
. State of a cache entry that does not currently contain a valid
copy of a cache block from memory.
Key bits
. A set of key bits referred to as Ks and Kp in each segment register
and each BAT register. The key bits determine whether supervisor or
user programs can access a
page
within that
segment
or
block
.
Kill
. An operation that causes a
cache block
to be invalidated.
Latency
. The number of clock cycles necessary to perform an action, such as
a memory access.
Least-significant bit (lsb)
. The bit of least value in an address, register, data
element, or instruction encoding.
Least-significant byte (LSB)
. The byte of least value in an address, register,
data element, or instruction encoding.
Little-endian
. A byte-ordering method in memory where the address
n
of a
word corresponds to the
least-significant byte
. In an addressed
memory word, the bytes are ordered (left to right) 3, 2, 1, 0, with 3
being the
most-significant byte
.
See
Big-endian.
Livelock
. A state in which processors interact in a way such that no processor
makes progress.
K
L