Glossary of Terms and Abbreviations
Glossary-1
Glossary of Terms and Abbreviations
The glossary contains an alphabetical list of terms, phrases, and abbreviations used in this
book. Some of the terms and deTnitions included in the glossary are reprinted from IEEE
Std 754-1985, IEEE Standard for Binary Floating-Point Arithmetic, copyright 1985 by
the Institute of Electrical and Electronics Engineers, Inc. with the permission of the IEEE.
Architecture.
A detailed speciTcation of requirements for a processor or
computer system. It does not specify details of how the processor or
computer system must be implemented; instead it provides a
template for a family of compatible
implementations
.
Asynchronous exception
.
Exceptions
that are caused by events external to
the processors execution. In this document, the term asynchronous
exception is used interchangeably with the word
interrupt
.
Atomic access
. A bus access that attempts to be part of a read-write operation
to the same address uninterrupted by any other access to that address
(the term refers to the fact that the transactions are indivisible). The
PowerPC architecture implements atomic accesses through the
lwarx
/
stwcx.
instruction pair.
BAT (block address translation) mechanism
. A software-controlled array
that stores the available block address translations on-chip.
Biased exponent
. An
exponent
whose range of values is shifted by a constant
(bias). Typically a bias is provided to allow a range of positive values
to express a range that includes both positive and negative values.
Big-endian
. A byte-ordering method in memory where the address n of a
word corresponds to the
most-signiTcant byte
. In an addressed
memory word, the bytes are ordered (left to right) 0, 1, 2, 3, with 0
being the most-signiTcant byte. See Little-endian.
Block
. An area of memory that ranges from 128 Kbyte to 256 Mbyte whose
size, translation, and protection attributes are controlled by the BAT
mechanism.
Boundedly undeTned
. A characteristic of certain operation results that are
not rigidly prescribed by the PowerPC architecture. Boundedly-
A
B