code taken from the MS-DOS operating system of the early 1980s, and that code looks for certain instructions when it boots.
This was part of the motivation behind Intel and Hewlett-Packard's EPIC project: a "clean-sheet" design that would remove many of x86's idiosyncrasies and support for legacy technologies, providing a modern foundation for the next 20 years.
Instead, EPIC became a lesson in how not to introduce a new instruction set. Software developers shied away from having to learn a new computing language, and early roll-out problems hindered Intel and HP's chances of building a broad market for the processor. The warm embrace of AMD's Opteron x86-64 processor (later duplicated by Intel) was the final blow, relegating EPIC and Itanium to the high end of the server market where it makes sense to port applications to take advantage of the performance offered by Itanium.
As with most things, it all came down to money. Billions of dollars have been invested in software written for x86. Even Intel--one of the most influential companies in the technology industry--couldn't convince software developers to move away from all those investments.
Is there an alternative?
Last year, Intel Chief Technology Officer Justin Rattner said the company had no plans to develop a new ISA in the foreseeable future. Microsoft's Rashid said his group doesn't have any projects that involve a rival instruction set, although Microsoft supported several different instruction sets as recently as 1999 with Windows NT 4.0.
So what might change the game? Performance is always one way to make software developers sit up and take notice, but there's nothing dramatic on the horizon. It's unlikely that any so-called "clean sheet" design would be able to produce more than a 10 percent improvement in performance or power consumption over the modern x86 ISA, Hester said.
A performance improvement that small isn't going to encourage a dramatic move away from x86, said Pat Gelsinger, a veteran chip designer and senior vice president and general manager of Intel's Digital Enterprise Group. "We're delivering 2x performance gains every year" with existing designs that can still run older applications.
The chip industry's ability to continue packing transistors onto its processors means that it dedicates fewer and fewer transistors--out of the whole--to keeping legacy code alive. "The burden of compatibility is there," Gelsinger said. "But the value of compatibility overwhelms the cost it brings with it."
One technology improvement that could be a wild card in the mix is the introduction of new chips with two or more processing cores. Chipmakers have settled on building chips with several lower-speed processor cores as a way of getting around power consumption problems caused by a single high-speed core. Right now, however, each core needs to use the same instruction set.
Some think a hybrid future is possible: smaller, more power-efficient cores could be created on an x86 using other ISAs that would be dedicated for specific tasks, like video processing, Arvind said.
IBM is doing something like this with its Cell processor design, found at the heart of Sony's PlayStation 3. Cell uses one PowerPC core in a sort of supervisory role over eight separate processing units. Further on down the road, chip companies could keep a basic x86 core to maintain backward compatibility and handle the next generation of complicated processing tasks with dedicated hardware--that may or may not run x86.
The earliest parts of this transition can be seen in efforts such as AMD's Fusion project, in which it plans to integrate a graphics processor onto a PC processor, McCarron said. By the next decade, processors with a mixture of cores using different ISAs could become a reality, he said.
But don't count on it.
"What has worked in (x86's) favor is that it's an evolutionary architecture, when problems come up it gets adapted," McCarron said. "This is ultimately the one that got picked. And for everything to work with each other, that's what we stick to."
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