By Jim Turley  |  Posted 2002-02-11 Print this article Print

: Going Out On a Limb"> The longer the pipeline, the bigger the train wreck if the processor mispredicts a branch. And Itanium has a fairly long pipeline, so the potential for performance-robbing disaster looms ever large. Predicting branches takes on paramount importance and to that end, IA-64 has a number of tricks to help it avoid the dreaded mispredicted branch. First, theres only one form of conditional branch, but its behavior can be based on any of the 64 predicate bits mentioned earlier. Branches can also be tagged with either static or dynamic branch prediction (thats prediction, not predication), which predicts whether the branch is likely, or not likely, to be taken this time around. Static prediction cannot be overridden; dynamic prediction leaves the decision to Itaniums own branch-prediction hardware. If you, as the programmer, know which way the branch is likely to go, stick with static prediction and the chip will assume youre always right. If youre unsure, let Itanium make up its own mind. If youre feeling especially clairvoyant, you can also suggest that Itanium fetch instructions from the predicted target of the branch, and even how far ahead of the branch target it should prefetch.

Jim Turley is a semiconductor industry analyst, editor, and presenter working in Silicon Valley. Focus technologies are 32-bit microprocessors and semiconductor intellectual property (SIP).

Most recently Jim was the Senior Vice President of Strategy & Technology at ARC International plc (LSE:ARK), where he set the Company's strategic direction and guided its technical developments at five locations worldwide. With headquarters in London (UK) and development centers in New Hampshire, Canada, and California, ARC International is an innovative leader in the semiconductor IP (intellectual property) industry.

Previously, Jim was senior analyst for MicroDesign Resources (a unit of Cahners/Reed Elsevier) as well as the Senior Editor of the prestigious industry journal Microprocessor Report (a three-time winner of the Computer Press Award), and Editor-in-Chief of Embedded Processor Watch. He also hosted and directed the yearly Embedded Processor Forum conference, the industry's annual showcase for new microprocessors. As an analyst and editor, Turley consulting with leading semiconductor firms, providing informed advice on technology trends and market requirements, and was often called on to participate in new product reviews, strategy sessions, and technology development for large semiconductor companies.

Turley is the author of six popular books including Advanced 80386 Programming Techniques, the best-selling PCs Made Easy and others published by McGraw-Hill and Academic Press. He's served as technical editor for several of McGraw-Hill's computer and programming books. In addition, he was a regular technology columnist for Embedded System Programming, Computer Design, and Supermicro magazines, and contributed articles to dozens more. Earlier in his career, Turley held engineering or marketing positions at Adept Technology, Force Computers, TeleVideo, and other high-technology firms in Europe and the United States.

Turley has created and presented numerous seminars and training sessions around the world covering technology trends and the competitive microprocessor market. He is also a well-known speaker at industry events such as the Embedded Systems Conference and Microprocessor Forum, is frequently quoted in the Wall Street Journal, New York Times, USA Today, San Francisco Chronicle, and San Jose Mercury News, and has appeared frequently on television, radio, and Internet broadcasts. Jim volunteers for Recording for the Blind and recently earned his amateur auto-racing license. He has a talented and stunningly attractive wife, two overachieving children, an apparently brain-damaged dog, and an opossum living under the house.

Jim can be contacted at or by calling (408) 226-8086.

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