13.2 How Implementations Change

While this book does not treat matters of hardware organization in any detail, our readers should pick up some awareness of the sorts of implementation differences that the Itanium, or any other, architecture may come to have over time. Major issues include technological feasibility, overall system performance, cost, and heat dissipation. The best technology does not always win, however. Favorable perceptions by opinion-makers, market acceptance, and the activities of competitors are also important influences.

As chip fabrication techniques are progressively refined to ever-smaller feature sizes, a given chip area can then be developed into more transistors. New implementations can use additional transistors in several ways:

  • to support additional instruction types, although this would break a strict definition of architectural conservatism;

  • to provide internal registers, invisible to the assembly language programmer, that can help alleviate data stalls in deeply pipelined execution units;

  • to increase the internal parallelism at the logic gate level in order to decrease the time in pipeline stages for operations such as propagation of carries in addition;

  • to provide hardware support for dynamic heuristics that reduce branch penalties;

  • to support larger page table sizes for operating systems;

  • to increase internal superscalar parallelism i.e., provide more execution units;

  • to increase the amount of on-chip cache for instructions and/or data;

  • to enable multithreading i.e., allow multiple software threads to execute in parallel within a superscalar processor, thereby keeping the execution units more fully occupied; and/or

  • to introduce a dual or multiple core i.e., put a capability for multiprocessing on the single chip where shared memory operations can be coordinated through the cache designs with extremely short signal path distances.

Some of these enhancements appeared in the Itanium 2 implementation, and many of them are likely to be considered over the lifetime of the Itanium architecture.



ItaniumR Architecture for Programmers. Understanding 64-Bit Processors and EPIC Principles
ItaniumR Architecture for Programmers. Understanding 64-Bit Processors and EPIC Principles
ISBN: N/A
EAN: N/A
Year: 2003
Pages: 223

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