Happy birthday, x86! An industry standard turns 30

Intel's x86 microprocessor architecture has dominated large swaths of computing for three decades. Here's why.

Ironically, the lack of software for RISC machines -- plus big performance gains on the 80486 and Pentium processors -- doomed Intel's i860 along with other RISC processors. Trying to introduce a second major microprocessor architecture was a mistake, Intel would later admit.

But RISC spurred much innovation, says David Patterson, a computer science professor at the University of California, Berkeley, and one of the key RISC innovators in the 1980s. "The [Digital Equipment Corp.] VAX architecture, for example, could not keep up with RISC, and it more or less disappeared. But Intel was able to incorporate the ideas that were becoming popular in RISC while maintaining their old architecture with its large software base. And they did that in part with their superior manufacturing."

The floating-point fiasco

Perhaps as gut-wrenching as the RISC threat was a crisis that began in the summer of 1994, when Intel test engineers discovered a tiny flaw in the floating-point division circuitry of its new Pentium chip. The flaw occurred so rarely and was so minor in its impact that Intel elected to just fix it and put the chip back into production without recalling the flawed chips.

But a few months later, Thomas Nicely, a math professor at Lynchburg College in Virginia, discovered the flaw in his PC. He was unable, Intel was to admit later, to find anyone at Intel who would even listen to his complaint. So he posted his findings on the Internet, and before long, Intel was engulfed in a firestorm of criticism that would ultimately lead to a public relations disaster and a $475 million recall of the chip.

"It was a painful rite of passage, but we finally learned to behave like a consumer company," recalls Albert Yu, a former Intel senior vice president, in his book, Creating the Digital Future .

Mixing and matching

Another defining moment in x86 history occurred in 1995, says Todd Mowry, a computer science professor at Carnegie Mellon University and an Intel research consultant. That's when Intel introduced the Pentium Pro, a microprocessor with some radical new features, such as the ability to look ahead in a stream of instructions, guess which ones would be needed and then execute them out of order. That kept the processor busy a larger percentage of time and, combined with a new, extremely fast on-chip cache, it offered huge performance gains in some applications.

"The thing that was radically different," Mowry says, "was that they used the benefits of RISC without changing the instruction set. They did that by translating the x86 instructions into micro-operations that are more like RISC instructions. So what you had was a RISC machine inside an x86 machine, and overnight, that eliminated the performance gap."

Mowry says the Pentium Pro resulted from a top-down design process. "They started out with the design of a fast machine and then figured out how to make the x86 run on it," he says.

That approach -- finding good ideas in non-x86 architectures and working backward from them -- was just how it worked, Gelsinger says. "The Pentium was a dramatic architectural leap. We took the best ideas from minis and mainframes and just implemented them better, because we had a superior canvas to paint them on, called silicon."

Unlike a mainframe, which spreads processing components over a wide area inside the box, putting everything on a single, tiny, tightly integrated chip gives microprocessor designers more flexibility and their designs more power, he says. Indeed, over the years, the performance of silicon chips has marched smartly along according to Moore's Law, while systems of interconnected components have not improved as fast.

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