Technical data

Glossary
control word operand: The portion of the instruction that indicates which
registers to use and enables or disables certain functions.
crossover point: The vector length at which the vector processor’s
performance exceeds that of the scalar processor.
data dependency: The case when data for one arithmetic instruction depends
on the result of a previous instruction so both instructions cannot execute at
the same time.
decomposition: Part of the compilation process that prepares code for parallel
or vector processing. It includes dependency analysis, recognition of parallel
or vector inhibitors, and code restructuring. Decomposition can be automatic
(controlled entirely by the compiler), directed (controlled by compiler
directives or statements in the source code), or by a combination of the
two.
dependency analysis: An evaluation of how data flows through memory. The
analysis is performed to identify data dependencies in a program unit and to
determine the requirements they place on decomposition.
first-order linear recurrence: A cyclic data dependency in a linear function
that involves one variable.
function unit: A section of the vector processor (or any other processor) that
performs a specific function and operates independently from other units.
Typically, a function unit performs related operations; for example, an add
function unit may also perform subtraction since the operations are similar.
Also called pipe.
gather: The collection of data from memory starting with a base address plus
an offset address; the instruction that performs this action placing the data
into sequential locations in a vector register.
integrated vector processor: A vector processor consisting of a coprocessor
that is tightly coupled with its host scalar processor.
interleaving: Using multiple memory boards in main memory so that one or
more processors can access data, that is distributed among different boards,
concurrently.
IOTA: An instruction to generate a compressed vector of offset addresses for
use in a gather or scatter instruction.
Glossary–2