AMD grabs high ground with SMP Athlon

AMD unveiled its multiprocessor plans yesterday, and judged solely on its technical merits, the Athlon-based SMPs that result ought to cause some late nights at Santa Clara. And not just of a tactical nature, but strategic. If we weren't so nasty and cynical, we'd be tempted to describe it as a technical tour de force that bears all the hallmarks of people who know how to build high bandwidth parallel systems. But judge for yourselves...

SMP AMD-style looks like this: there'll be basic two way or four way building blocks, again using the 266Mhz Athlon bus, based on the new AMD-760 MP chipset. Level 1 cache is exclusive, and the front-side "bus" (yes, OK, we know it's a switch...) hums along at 4.2GBytes/second. Nothing to worry the Alpha folks there just yet, but Athlon's deep pipelines and other judicious design choices - such as a dedicated snoopy bus - leave an awful lot of headroom for the architecture. Chimpzilla also reckons that adding an "owner" state to the cache coherency protocol also optimizes inter-cache traffic ... but we'll throw this one to the floor.

AMD veep Rich Heye, a veteran engineer of both the early DEC Alpha and IBM Somerset Project (aka, the PowerPC) - unveiled the details with a marvellous fusillade of one liners, the most popular of which had some Intel folk grinning: "They said we couldn't do it [Athlon]... but we built it, we shipped it... and we didn't have to recall it."

Catching him in an off-guard moment later, Heye (a Reg devotee, natch) pinned the blame on Intel's fetish for the Rambus architecture. AMD's SMP uses DDR.

"I haven't seen P4," he said, "but the whole point of this is to keep banging the memory with requests. I'll bet you that with Rambus, most of the time those buffers are empty." Heye made the same point, anticipating a forthcoming clock speed bus war in the presentation:

"Some people will look at bus speeds and say, 'Aw, 266Mhz? That's as slow as sin'. But you can't just be looking at wire speeds or at clock rates - it's how you use those wires," he said.

Which is fine by us. But of course there's a lot more to building SMPs than filling pipelines. Throughout its succession of well-publicised recalls, Intel's front edge server business continued to do its usual, awesome job of providing reliable SMP racks in large numbers and to order. That makes AMD's next challenge an operational, rather than technical issue.

But where it gets strategic and really serious for Chipzilla is that the volumes in the low-end server business are that much lower than in the volume desktop business. With their respective fab capacities, AMD has, regardless of what it might like to do, a practical ceiling for its market share. But the two way/four way business looks a lot more promising, and really becomes low-hanging fruit for AMD. A successful roll-out of the first racks could see AMD gobble up a greater proportion of the business quite rapidly. Whether it has the operational expertise to seize this new channel, we'll see. ®