The server market has been AMD's bread and butter for the past few years, and it has been the place that the company has really remained competitive with Intel. AMD's mobile strategy has mainly involved using versions of its server parts to target the low-cost laptop market, so the company has missed out on the netbook revolution of the past few years.

With the launch of products based on its new mobile architecture, codenamed Bobcat, AMD will finally join Intel in having two separate architectural families: one for servers and desktops, and another ultra-low-power design for mobiles. Bobcat, then, is AMD's answer to Intel's Atom, but instead of targeting where Atom is now, the company has chosen to target where Atom is likely to be in the not-so-distant future.

Like Atom, but faster (and hotter)

In a nutshell, Bobcat looks like a more advanced, out-of-order version of Intel's Atom design. Atom, you'll recall, has a relatively primitive in-order architecture that harks back to the era before the Pentium Pro. The fact that Atom is in-order and lacks an instruction window, which modern processors use to dynamically optimize the flow of code through the machine's back-end, means that the design performs quite poorly on the kind of integer code that makes up most of the installed x86 codebase. In fact, Atom performs so poorly on ordinary Windows OS and application code that it's inevitable that Intel will, at some point, introduce out-of-order execution into the Atom family.

AMD's Bobcat, pictured in the slide below, has essentially the same dual-issue design as Atom, but with the all-important instruction window (a reorder buffer plus queues for integer and floating-point ops) added in. Also present are integer and floating-point/SIMD rename registers, which eliminate some load-store traffic and go hand-in-hand with the instruction window in letting the machine juggle instructions on-the-fly so that stalled instructions can be worked around.

The end result is that, where Atom is something like an original Pentium with a large floating-point/SIMD block added on, Bobcat moves into Pentium Pro territory. Of course, neither Bobcat nor Atom have the same execution-core breakdown (i.e., two asymmetric integer pipelines, a load pipe, a store pipe, and two asymmetric floating-point/SIMD pipes) as anything that has come before, so we're speaking very generally with the Pentium/PPro analogies.

The inclusion of an instruction window and associated hardware is going to cost Bobcat quite a bit in terms of power, because the instruction window is generally very costly from a power standpoint. The reason for this is not so much because the instruction window's hardware takes up a lot of space in the floor plan, but because it's hardware that's on all the time. Different parts of the front- and back-end of a processor can be shut off when not in use, but the instruction window is never "not in use." As such, it's a classic "hot spot" on a chip, and it represents a huge power burden. This is why Intel chose to leave it out for Atom.

Like Intel's Core family of processors, Bobcat can also do some amount of memory reordering. This was probably a good place to spend transistors because it can boost performance without being the kind of hardware that will necessarily stay active.

Odd won out

Ultimately, it's a bit hard to locate this design within the context of the current market. On the one hand, it's an amazingly straightforward architecture of the kind that could have easily been made in the first half of the decade. But on the other hand, nobody ever really produced a design that was this totally straightforward, in the sense that it has two integer pipes, two address pipes, and two floating-point/SIMD pipes. Designs from Intel, AMD, and IBM have had different divisions of labor in the back-end, but nothing that breaks down in the way that Bobcat does.

This is probably because all the other designs of similar complexity are three-issue or higher, so they structure their back-end very differently. In this sense, Bobcat has the largest amount of back-end hardware of any dual-issue processor we've ever seen, which has to make it unbalanced. With this amount of execution hardware, Bobcat should really be three-issue at least (two integer and one FP/SIMD per clock), but it just doesn't have the front-end hardware. It's also the case that increasing the issue width would have increased the size (and power consumption) of the instruction window.

Ultimately, the fact that it's so odd makes it hard to predict how Bobcat will perform on different types of code. Obviously, Bobcat will smoke Atom clock-for-clock in raw performance, but the performance per watt picture is a bit less clear. This is because it is quite apparent that AMD will have a harder time keeping its power consumption down than Intel does with Atom.

Bobcat's architecture also makes it clear that AMD doesn't really have any immediate designs on the "embedded" market the way that Intel does, because Bobcat just will not shrink down into the same variety of SoC implementations that Atom will. Bobcat is more of a threat to Atom in the netbook and laptop segments than it is in the kinds of appliance-type niches that Intel is now aiming its Atom-based SoCs at. And nobody is going to try to squeeze Bobcat into a smartphone form factor anytime soon, the way that Intel is trying to do with Atom.

Bobcat in the datacenter?

Once place where Bobcat could potentially compete with Atom is in the emerging market for low-cost, low-power, high-density cloud servers. If AMD can keep Bobcat's power consumption and cost down, it could have a shot at this market.

We asked AMD's Dina McKinney, vice president of design engineering, point-blank if AMD saw any role for Bobcat in the datacenter, and she tried to dodge the question so we asked her again, at which point she just reiterated AMD's commitment to the netbook market and left the server idea at, "we'll see where market trends take us."

The takeaway from that exchange was that AMD's messaging around Bobcat is 100 percent about netbooks and laptops, and that McKinney was sticking to the message. So it's still not clear what, if any, server plans AMD has for Bobcat.

A reader e-mailed us to point out that Bobcat has ECC in its L2 cache, which could suggest that AMD may see a datacenter role for the part. But then again, Atom has this as well, so it's not really much of an indicator of AMD's plans.

So while the cloud datacenter market may have some potential for AMD, Bobcat seems to be very much aimed strictly at Windows netbooks and laptops—not phones and TVs and other SoC-friendly applications, and probably not at cloud data centers. AMD may score some design wins with Bobcat in these latter two categories, but Bobcat will be strongest in the more traditional mobile roles for which it was designed.