Apple PowerPC G5 User Manual
PowerPC G5
The World’s First 64-Bit Desktop Processor
White Paper
July 2003
Contents
Page 3 Introduction
Page 4 The World’s First 64-Bit Desktop Processor
An Exponential Leap in Computing Power
Memory Addressing up to 18 Exabytes
High-Precision Calculations in a Single Clock Cycle
Clock Speeds up to 2GHz
Industry-Leading 1GHz Frontside Bus
Full Support for Symmetric Multiprocessing
Native Compatibility with 32-Bit Application Code
Page 7 Next-Generation PowerPC Architecture
Ultrafast Access to Data and Instructions
Highly Parallel Execution Core
Aggressive Queuing and Register Renaming
Optimized 128-Bit Velocity Engine
Two Double-Precision Floating-Point Units
Two Integer Units
Two Load/Store Units
Condition Register
Three-Component Branch Prediction Logic
State-of-the-Art Process Technology from IBM
Page 11 Industry-Leading Performance
SPEC CPU2000
Page 14 Technical Specifications
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Introduction
The revolutionary PowerPC G5 changes everything you know about personal computing.
Suddenly, the next generation of high-performance applications for design and graphics,
media production, and scientific research is possible and practical on the desktop. That’s
because the PowerPC G5 brings a 64-bit architecture to the Mac platform—ushering in
an exciting new era in personal computing.
The introduction of the PowerPC G5 is a product of Apple’s partnership with IBM, leveraging the most advanced chip design and manufacturing expertise in the world. The
results are phenomenal: 130-nanometer fabrication technology, 2GHz clock speeds, and
an all-new PowerPC architecture.Together, they put enormous computing power within
the reach of personal computer users:
•The ability to address huge amounts of memory provides ultrafast data access, boosting
performance for 2D imaging, 3D design, and video rendering tasks.
•A high-bandwidth execution core with 12 functional units improves performance by
executing multiple instructions per cycle in parallel.
•An optimized 128-bit Velocity Engine cranks through image editing tasks, highdefinition video transitions, and complex scientific analysis.
•Two double-precision floating-point units accelerate 64-bit calculations for 3D
visualization, research simulations, and multitrack audio creation.
The G5 processor is making its debut in the Power Mac G5, the world’s fastest personal
computer according to industry-standard SPEC benchmarks.
1
Now Power Mac users can
tackle projects never before possible on a desktop system—and blaze through their
work faster than ever. In fact, the Power Mac G5 runs Adobe Photoshop more than two
times faster than the fastest Pentium 4–based system.
2
Best of all, the PowerPC G5 runs
32-bit code—including existing Mac OS X applications—natively, so the transition to
64-bit power is absolutely seamless.
Welcome to the PowerPC G5, the world’s first 64-bit desktop processor and the heart
of the new Power Mac.
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Key Features
•64-bit architecture, capable of addressing
18 exabytes of memory
•Clock speeds up to 2GHz
• 1GHz frontside bus for throughput of up to
8 GBps per processor
•Dual independent 1GHz frontside buses in
dual processor systems
• Superscalar execution core supporting up to
215 in-flight instructions
•Velocity Engine for accelerated singleinstruction, multiple-data (SIMD) processing
•Two double-precision floating-point units
for high-speed advanced computation
•Massive three-component branch prediction
logic to increase processing efficiency
•Native compatibility with existing 32-bit
application code
•State-of-the-art process technology
from IBM
The World’s First 64-Bit
Desktop Processor
The PowerPC G5 marks the arrival of 64-bit performance to the personal computer
market. With 64-bit-wide data paths and registers, this groundbreaking new processor
can address vast amounts of main memory and handle multiple large integer and
floating-point math calculations in a single clock cycle.
An Exponential Leap in Computing Power
The label “32-bit” or “64-bit” characterizes the width of a microprocessor’s data stream,
which is a function of the sizes of its registers and the internal data paths that feed the
registers. A 64-bit processor moves data and instructions along 64-bit-wide data paths—
compared with the 32-bit-wide paths on 32-bit processors, such as the Pentium 4. In
addition, 64-bit processors have wide registers that can store 64-bit numbers as well
as 32-bit numbers.
The leap from 32-bit to 64-bit processing represents an exponential advance in computing power. With 32-bit registers, a processor has a dynamic range of 2
32
, or 4.3
billion—which means it can express integers from 0 to 4.3 billion. With 64-bit registers,
the dynamic range catapults to 2
64
, or 18 billion billion—4.3 billion times larger than
the range of a 32-bit processor.
Memory Addressing up to 18 Exabytes
The move to 64-bit processing results in a similarly dramatic leap in the amount of
memory supported. A memory address is a special kind of integer, and each address
points to one byte in memory. Since memory addresses are computed in 64-bit registers
capable of expressing 18 billion billion integers, the PowerPC G5 can theoretically
address 18 exabytes (18 billion billion bytes) of virtual memory.
In practice, memory addressing is defined by the physical address space of the processor.
The PowerPC G5, with 42 bits of physical address space, supports a colossal 2
42
bytes,
or 4 terabytes, of system memory. Although it’s not currently feasible to purchase 4 terabytes of RAM, very large quantities of memory enable a desktop system to contain a
gigantic 3D model, a complex scientific simulation, or a sequence of HD video entirely
in RAM—drastically reducing the time to access, modify, and render the data.
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4.3 billion times bigger
To grasp the exponential leap from 32-bit to
64-bit processing, imagine equating the range
of numbers a processor can express with a
two-dimensional area. A 32-bit processor can
express a range of integers equal to the size
of a postcard, while a 64-bit processor can
express a range of integers larger than the
island of Manhattan.
32-b
it processing
Post card =
24 in.2 (155 cm2)
64-bit processing
Manhattan =
2
22 mi.
(57 km2)
High-Precision Calculations in a Single Clock Cycle
With 64-bit-wide data paths and registers, the PowerPC G5 can execute instructions
on 64 bits of data in a single clock cycle—making it possible to perform huge integer
calculations and highly precise floating-point mathematics. In contrast, a 32-bit processor would have to split up any data larger than 32 bits and process it over multiple
clock cycles. The advanced calculation capability of the PowerPC G5 is critical in stateof-the-art applications for scientific simulations, 3D modeling, and video effects.
Clock Speeds up to 2GHz
The PowerPC G5 features a scalable design that enables it to run at clock speeds
up to 2GHz. This represents a 600MHz jump, the largest in PowerPC history, over the
fastest G4 processor at 1.4GHz. What’s more, this breakthrough clock speed boosts
performance across the board, accelerating everything from gaming frame rates to
digital audio effects.
Industry-Leading 1GHz Frontside Bus
To harness the power of the G5 processor, a 64-bit Double Data Rate (DDR) frontside
bus maximizes throughput between the processor and the rest of the system. Unlike
conventional processor interfaces, which carry data in only one direction at a time, the
PowerPC G5 features two dedicated unidirectional 32-bit data paths (64 bits total): One
travels into the processor and one travels from the processor, with no wait time while
the processor and the system controller negotiate which will use the bus or while the
bus switches direction. In addition, the data streams integrate clock signals along with
the data—allowing the frontside bus to work at speeds up to 1GHz for an astounding
8 GBps of total bandwidth.
In dual PowerPC G5 systems, each processor has its own discrete 1GHz frontside bus.
Theresult is a maximum aggregate bandwidth of 16 GBps on dual 2GHz Power Mac
G5 systems, well over twice the 6.4-GBps maximum throughput of Pentium 4– or
Xeon-based systems. In addition to providing fast access to main memory, this highperformance frontside bus architecture enables each PowerPC G5 to discover and
access data in the other processor’s caches—a process called intervention. Cache
intervention is made possible by cache coherency, which ensures that the processor
always fetches the correct data, even if it has been modified and is in L2 cache.
Full Support for Symmetric Multiprocessing
The PowerPC G5 is designed for symmetric multiprocessing—enabling multiple
applications to run independently on different processors or a single multithreaded
application to perform multiple tasks simultaneously. For example, while performing
an edit, Final Cut Pro can decode two pieces of source video, one on each processor,
at the same time.
With dual independent frontside buses and built-in cache coherency, a dual processor
system manages priorities between the two processors for maximum efficiency. And
since Mac OS X was built from the ground up for symmetric multiprocessing, no special
optimization is required for software to take advantage of this powerful capability.
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The bidirectional frontside bus allows data to
travel to and from the PowerPC G5 processor
at the same time. In dual processor systems,
each PowerPC G5 has its own dedicated interface to maximize throughput—compared
with dual Xeon-based systems, which force
the processors to share a single bus.
PowerPC G5 PowerPC G5
Xeon Xeon
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