AMD's New Architecture: It's More Than Just 64-Bit Extensions

To outsiders, the hallmark of the AMD64 hybrid 32/64-bit architecture is its 64-bit instruction set extensions. But to company executives, that's only a small part of the story of the Opteron server processor and its cousin, the Athlon 64 desktop chip.

"When we looked at AMD64 technology, we looked at more than just the instruction set and the memory addressability," says Patrick Patla, Opteron marketing manager at AMD. "We looked at all the features of the system architecture and enhanced those to make sure that they were going to be in line to take full advantage of the 64-bit extensions."

That complete package is called the Direct Connect Architecture (DCA), in AMD parlance.

Most immediately apparent are the extensions, which enable software applications to take advantage of a set of 64-bit addressing and data registers on board the chips. The wider addressing registers enable the processors to exceed the 32-bit memory limit of 4 GB. That makes the processors ideal for use by large-scale database and server applications.

But a crucial element of DCA is the ultra-fast memory controller AMD has placed on board the chips."Integrating the memory controller onto the CPU core was key, because 50 percent of the cost of a server is memory," Patla explains. "The No. 1 thing you can do to enhance server performance is give it the best possible memory controller and the best possible memory performance."

Placing the controller on chip means memory accesses are more direct and don't have to traverse a traditional Northside bus.

AMD also makes certain customers understand that it didn't simply slap 64-bit registers onto an existing 32-bit architecture to create AMD64. "The value proposition here is not just 64 bits," says Kevin Knox, AMD's director of worldwide enterprise business development. "It's a superior 32-bit architecture."

In answering back at AMD, Intel is taking a two-pronged approach. It has fielded its own 32/64 Xeon (formerly code-named Nancona), which includes Intel instruction-set extensions that are compatible with AMD's. At the high end of the server market, Intel offers a full 64-bit processor called Itanium (see "Itanium Still the 64-Bit Jewel In Intel's Crown," page 50).

Intel positions the new Xeon as one component of its balanced platform. "We're recommending that people treat 64-bit extensions as just one of a collection of good things that you're going to start seeing in Intelplatforms targeted at servers and workstations," says Jerry Braun, Intel's product line manager for Xeon volume processors.

The important surrounding technologies, he says, are the next-generation PCI Express point-to-point I/O channel and Double Data Rate 2 (DDR2) memory.

Moving forward, reports are bubbling up from the field that Intel may answer back at AMD by adding its own on-board memory controller into a 64-bit-capable Xeon. Intel's Braun declined to comment about that. Such a move would enable Intel to effectively claim on-chip feature parity with Opteron--something it claims it doesn't want to do.

"We'll continue to innovate at the platform level," Braun emphasizes.