Instruction Set Highlights

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

It would be tedious in the extreme to even summarize the entire IA-64 instruction set; you can refer here for the complete ISA (Instruction Set Architecture) listing. But there are some highlights in the ISA worth noting, such as conditional (predicated) execution, hinted and speculative loads, and the odd way in which Itanium handles integer math. Pretty much any IA-64 instruction can be conditional, with its execution predicated on literally anything you care to define. Far beyond the simple Z (zero), V (overflow), S (sign), and N (negative) flags of our childhood, IA-64 has 64 free-form predicate bits, each considered a separate predicate register. You can set or clear a predicate bit any way you like, and its condition sticks indefinitely. Any subsequent instruction anywhere in the program can check that bit (or multiple bits) and behave accordingly. This allows you, for example, to evaluate two numbers in one part of a program, but not make a decision (conditional branch) until much later. The microprocessor cognoscenti consider predicate bits more elegant than flags; they scale more easily to larger sizes (more bits) and are easier for compilers to target. Well cover predication in more detail below.

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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