Apple Power Mac G5 (Late 2005) Bedienungsanleitung PDF herunterladen (Seite 8)

Technology Overview

Power Mac G5

Eight Double-Precision Floating-Point Units

The PowerPC G5 core contains two double-precision ﬂ oating-point units, each capable

of performing a multiply and an add at the same time. This means a Power Mac G5

Quad, with four processor cores and a total of eight ﬂ oating-point units, can complete

up to sixteen 64-bit ﬂ oating-point operations in a single cycle.

Such immense 64-bit computational power accelerates applications in many ﬁ elds,

including audio creation, 3D content creation, and scientiﬁ c visualization and analysis—

resulting in performance levels far beyond those of previous Power Mac generations.

Fused multiply-add example

The ﬂ oating-point units in the PowerPC G5 can complete both a multiply and an add

operation as part of the same machine instruction—accelerating matrix multiplication,

vector dot products, and other scientiﬁ c computations. Referred to as fused multiply-

add, or “fmadd,” this instruction is considered a building block for data-intensive

ﬂ oating-point computation.

The following computation can be completed by a fused multiply-add instruction in

one pass through either of the two ﬂ oating-point units in a PowerPC G5 core:

T = (a * b) + c

On other processors, two instructions are required. The ﬁ rst is a multiply instruction:

U = (a * b)

The product “U” is used by a second instruction, an addition, to complete the

computation:

V = U + c

In processors with comparable clock speeds, the computation of “(a * b) + c” is com-

pleted twice as fast using fused multiply-add. It also delivers a more accurate result,

because round-o∂ occurs just once in the computation of “T”—while on other proces-

sors, round-o∂ occurs twice: in the computation of “U” and in the computation of “V.”

Four Velocity Engine Units

A dual-pipelined Velocity Engine in each processor core is optimized with two inde-

pendent queues and dedicated 128-bit registers and data paths for e∑ cient instruction

and data ﬂ ow. This 128-bit vector processing unit accelerates data manipulation by

applying a single instruction to multiple data at the same time, known as SIMD pro-

cessing. Originally implemented in the PowerPC G4, the Velocity Engine in the PowerPC

G5 uses the same set of 162 instructions, enabling it to accelerate existing Mac OS X

applications that have been optimized for the Velocity Engine.

Vector processing is useful for transforming large sets of data, such as manipulating an

image or rendering a video e∂ ect. For example, when a designer uses a ﬁ lter to apply

a motion blur to an image, each pixel of the image must be changed according to

the same set of instructions—a highly repetitive processing task. Each Velocity Engine

pipeline speeds up this task by processing up to 128 bits of data, in four 32-bit integers,

eight 16-bit integers, sixteen 8-bit integers, or four 32-bit single-precision ﬂ oating-point

values, in a single clock cycle. That works out to 16 simultaneous 32-bit ﬂ oating-point

operations on a Power Mac G5 Quad.

Linpack

A measure of a computer’s ﬂ oating-point

execution performance, the Linpack

benchmark solves a dense system of linear

equations. The Power Mac G5 Quad executed

the double-precision equations 88 percent

faster than the dual 2.7GHz Power Mac G5

and an amazing 626 percent faster than the

dual 1.42GHz Power Mac G4.

Gigaﬂ ops

The gigaﬂ ops test indicates a system’s

vector processing capability by measuring

the maximum number of ﬂ oating-point

operations it can perform. With four Velocity

Engine units, the Power Mac G5 Quad

completed the test 85 percent faster than the

dual 2.7GHz Power Mac G5 and 260 percent

faster than the dual 1.42GHz Power Mac G4.

11.1 gigaﬂops

Power Mac G5

Quad 2.5GHz

21 gigaﬂops

Dual 2.7GHz

Power Mac G5

2.9 gigaﬂops

Dual 1.42GHz

Power Mac G4

41.1 gigaﬂops

Power Mac G5

Quad 2.5GHz

76.6 gigaﬂops

Dual 2.7GHz

Power Mac G5

21.3 gigaﬂops

Dual 1.42GHz

Power Mac G4

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