Apple Power Mac G5 (Late 2005) Bedienungsanleitung PDF herunterladen (Seite 7)

Technology Overview

Power Mac G5

Bidirectional Frontside Bus

Leveraging the dual frontside bus architecture pioneered in the original Power Mac

G5, each dual-core processor has an independent data path to the system controller

running at up to 1.25GHz. Unlike conventional processor interfaces, which carry data

in only one direction at a time, this dual-channel frontside bus has two 32-bit point-

to-point links (64 bits total): One link travels into the processor and another travels

from the processor, which means no wait time while the processor and the system

controller negotiate which will use the bus or while the bus switches direction. This

enables data to move in opposite directions simultaneously—a dramatic improvement

over previous processor interfaces.

In Power Mac G5 Quad systems, each processor has its own bidirectional interface

to the system controller, unlike traditional dual-processor systems, which constrain

throughput by placing all processor resources on one bus. Each G5 processor has

a dedicated interface to main memory for total bandwidth of up to 10 GBps per

processor, or a total of 20 GBps for a quad system. This high-performance frontside

bus architecture also enables each core to discover and access data in the other cores’

caches—further increasing performance on quad-core systems.

64-Bit Processor Architecture

The dual-core PowerPC G5 joins forces with Mac OS X v10.4 Tiger to enable 64-bit

computation, including the ability to address vast amounts of main memory and to

perform double-precision ﬂ oating-point calculations.

Support for massive amounts of memory

The move to 64-bit processors results in a dramatic leap in the amount of memory

supported. In practice, memory addressing is deﬁ ned by the physical address space

of the processor. The PowerPC G5, with 42 bits of physical address space, supports a

colossal 2

bytes, or 4 terabytes (4TB), of system memory. Although it’s not currently

feasible to purchase 4TB of RAM, the advanced architecture of this processor allows

for plenty of growth in the future.

More practical and still far more than a typical PC, the Power Mac G5 can be conﬁ g-

ured with 16GB of addressable memory. Such large quantities of memory enable the

system to contain a complex 3D model, massive digital images, a scientiﬁ c simulation,

or a sequence of video entirely in RAM. When data is stored in memory, the processor

can access it 40 times faster than from the hard drive, drastically reducing the time

to manipulate, modify, and render the data and making it feasible to tackle gigantic

projects on a desktop system.

64-bit computation power

The other advantage provided by the 64-bit PowerPC G5 is the ability to perform

multiple simultaneous 64-bit ﬂ oating-point and integer calculations. The PowerPC

G5 features full 64-bit data paths and data registers, allowing it to express the extreme

precision needed for ﬂ oating-point mathematics and to express integers up to 18 billion

billion. By contrast, a 32-bit processor must break these types of computations into

multiple pieces—requiring multiple passes through the processor and slowing down

application performance.

In Power Mac G5 Quad systems, each

dual-core PowerPC G5 processor has its

own bidirectional frontside bus.

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