The Parallel Universe: Opening
the Door
A meta-discussion about the Itanium Architecture
John Worley, System Architect
Secure64
10.09
DELIVERING A NEW ERA IN MISSION-CRITICAL COMPUTING
Copyright © 2009, Itanium® Solutions Alliance. All rights reserved.

Power of Itanium architecture
An impressive set of innovations:
• Large register sets
• Explicit parallelism
• Predication
• Register Rotation
• Rich, well-designed ISA
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DELIVERING A NEW ERA IN MISSION-CRITICAL COMPUTING
Copyright © 2009, Itanium® Solutions Alliance. All rights reserved.

Ongoing Itanium critique
Negative comments group into 3 categories:
• Speed
• Compatibility
• Utility
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DELIVERING A NEW ERA IN MISSION-CRITICAL COMPUTING
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Speed
“It doesn’t run as fast as Pentium”
• CPU frequency is a performance dead-end
• Silicon can’t be made to go faster, details
like power and cooling make it nonviable
• Only way to increase CPU performance is to
increase amount of useful work done each cycle
• Out-of-order techniques quickly run into
a combinatorial wall (tricky to exploit in
practice
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DELIVERING A NEW ERA IN MISSION-CRITICAL COMPUTING
Copyright © 2009, Itanium® Solutions Alliance. All rights reserved.

Itanium a multi-core winner
Puts instruction scheduling in the hands of software
and uses chip real estate for real performance
winners:
• Large register sets minimize memory access
• Huge on-chip caches for faster memory access
when needed
• Branch elimination and managment to keep
pipelines running smoothly
• Rich, powerful ISA
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DELIVERING A NEW ERA IN MISSION-CRITICAL COMPUTING
Copyright © 2009, Itanium® Solutions Alliance. All rights reserved.

Compatibility
“It’s not compatible with Pentium”
• So what? Pentium wasn’t compatible with the VAX and
that wasn’t compatible with IBM 370 and so on...
• There are many thriving CPU architectures as they have
been creations of trade-offs:
• Transistor counts
• Critical path lengths
• Target workloads
• Power
• Other application and environment variables
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DELIVERING A NEW ERA IN MISSION-CRITICAL COMPUTING
Copyright © 2009, Itanium® Solutions Alliance. All rights reserved.

Utility
“It’s too hard to use”
• Early compilers were a disappointment, but this has
improved markedly over the years
• Regardless of language, compilers aren’t enough, as
difficulties persist:
• Syntactic constraints
• Semantic constraints
• Loss of high-level information when converting from
the human thought process a sequence of machine-
friendly steps
• Only by blending a detailed knowledge of the underlying
architecture with high-level understanding of the problem
that best possible performance can be achieved
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DELIVERING A NEW ERA IN MISSION-CRITICAL COMPUTING
Copyright © 2009, Itanium® Solutions Alliance. All rights reserved.

Itanium is a tool to explore
computing in the Parallel Universe
Itanium changes the rules for programs and
programmers - we have to reconsider:
• Methods
• Algorithms
• Tools
• Approaches
The challenges are great, but the rewards are
greater still
8
DELIVERING A NEW ERA IN MISSION-CRITICAL COMPUTING
Copyright © 2009, Itanium® Solutions Alliance. All rights reserved.

Thank You
John Worley, System Architect
Secure64
http://www.secure64.com/
9
DELIVERING A NEW ERA IN MISSION-CRITICAL COMPUTING
Copyright © 2009, Itanium® Solutions Alliance. All rights reserved.