Intel is a company famously driven by paranoia, but the threat it now faces requires no special effort to see. Smartphones have grown and morphed into tablets, and together, these two new categories of devices have taken a big bite of out the consumer computing market. Laptop sales in particular have gone soft as tablets have grown in popularity.
The vast majority of these tablets are based on CPU technology from ARM. Intel’s position in the PC market couldn’t be much more commanding right now, but that alone is suddenly looking like a wobbly foundation for the future. The firm has attempted to address the mobile market with successive generations of its Atom processors, but those haven’t seen much success. Now, a rising urgency has prompted Intel to double down on its efforts, much as it did when the Pentium 4 was struggling to keep pace with AMD’s chips. For the first time, the years-old Atom microarchitecture has been completely rebuilt, and Intel has committed to bringing its methodical tick-tock development cadence to the Atom lineup going forward. Architectural refreshes will be interleaved with new process technology in a series of yearly updates.
Each of these updates will produce a host of Atom-based systems on a chip (SoCs) for different markets. The eight-core chip known as Avoton is headed for microservers and storage applications. Its near-identical twin, Rangeley, will be deployed in network and communications devices. An SoC called Merrifield will tackle the smartphone space.
Our concern today is the chip intended for tablets and convertible laptops, which is code-named Bay Trail. We’ve known for a while that Bay Trail was coming and that it would be based on the new Silvermont CPU microarchitecture. Beyond that, details have been scarce. Now, as the Intel Developer Forum opens in San Francisco, Bay Trail is making its first public appearance. We have extensive details on the SoC’s basic architecture—and a first look at its performance.
An overview of the SoC
A shot of the Bay Trail die. Source: Intel.
Bay Trail truly is a system on a chip, with a full complement of the components needed for laptops and tablets. It is in many ways similar to the Avoton chip we covered last week, but Bay Trail is scaled back for a smaller footprint, lower power use, and lower costs.
Like Avoton, Bay Trail is fabricated on a special variant of Intel’s 22-nm manufacturing process that’s been tuned for SoCs. This process has some of the finest geometries in the industry and is the first to implement a tri-gate or FinFET-style transistor structure. The foundries that produce ARM-based SoCs for competitors like Qualcomm and Nvidia are arguably at least a couple of years behind Intel on this front—and Intel is already talking about making the transition to 14 nm next year.
Below is a simplified block diagram of the Bay Trail SoC. We can use it as a starting point and add some detail to get a pretty good picture of what’s included in the silicon.
Logical block diagram of the Bay Trail SoC. Source: Intel.
The four CPU cores probably deserve top billing. The Silvermont architecture clumps two cores together into a single “module” that functions as a basic building block. Each module has 1MB of L2 cache shared between its two cores, and Bay Trail integrates two of these modules. We’ve already covered the Silvermont microarchitecture in some depth. The big change here is a focus on higher per-thread performance. Silvermont does away with symmetric multithreading (aka Hyper-Threading) and instead adds out-of-order execution in an effort to extract more parallelism out of sequential code. This change is eminently sensible given that the performance of one or two main threads often determines the user experience in tablets—and that even a relatively small chip like Bay Trail can execute four hardware threads without SMT.
At the center of the “north complex” above is an orange block known as the Silvermont system agent. The SA is the traffic cop that directs the flow of data between the major functional blocks of Bay Trail’s north complex. We know from our look at Avoton that the system agent employs a crossbar architecture, like a network switch, to ensure high-bandwidth communication from any one component to any other. The SA is linked to the Silvermont modules using a point-to-point interface known as IDI; it’s the same interface Intel has used in its big cores since Nehalem.
Hanging off of the system agent are Bay Trail’s dual memory controllers, each capable of talking to a single channel of DDR3 or DDR3L memory. The chip’s peak possible memory bandwidth is about 17 GB/s when both channels are equipped with 1066 MT/s memory. I assume this relatively low memory speed is due to power considerations. Some variants of Bay Trail will support only a single memory channel, and in that case, the DRAM can run at 1333 MT/s.
With both channels populated, the SoC’s maximum memory capacity is only 4GB, another indication of this platform’s power and size constraints.
One of the largest areas on the Bay Trail die is dedicated to graphics. Interestingly, Intel has jettisoned the Imagination Tech graphics it used in prior generations of mobile SoCs in favor of its own in-house Intel HD Graphics. This is essentially Intel’s latest graphics tech, and it’s the same generation used in larger Ivy Bridge CPUs. (Haswell’s graphics hardware is similar but tweaked for higher efficiency.) Intel says Bay Trail supports the latest graphics APIs, including DirectX 11 and OpenGL ES 3.0. We know from Ivy Bridge that this graphics core supports high-precision datatypes and is capable of general-purpose computing via OpenCL.
Of course, the unit count has been scaled back for this mission. Haswell desktop processors like the Core i7-4770K have 20 graphics executions units, or EUs. Bay Trail has only four EUs. For those keeping score at home, each of those EUs is SIMD32, equivalent to eight “shader processors” in the world of big GPUs, so Bay Trail has the equivalent of 32 SPs. The graphics clock speed varies but can reach as high as 667MHz in optimal conditions. According to Intel, that should add up to three times the performance of Clover Trail, its prior-generation tablet SoC.
Bay Trail’s video processing block can decode an alphabet soup of modern video formats, including H.264, VC1, MPEG2, and MPEG4. The hardware can also encode video in a couple of formats. H.264 encoding is accelerated fully, while MPEG2 encoding is handled via a hybrid approach, with key portions like motion estimation offloaded to hardware and other parts handled in software.
The display controller is fairly beefy, as it will need to be in order to drive the high-density displays now popular in tablets. The chip has two matching display outputs that conform to a range of standards, including HDMI 1.4, DisplayPort 1.2, DVI, and eDP 1.3. Each one can drive a display with a resolution of up to 2560×1600 at a refresh rate of 60Hz.
Oh, and here’s a feature with a classic Intel-style name: Display Power Saving Technology, or DPST for short. This feature combines dynamic backlight dimming with image modification (brightening up the images, basically) in order to reduce the power consumed and the heat produced by the display backlight—presumably without the end user noticing.
The final feature of the north complex is an image signal processor, which controls any onboard cameras and both receives and processes the pixels they capture. Bay Trail’s ISP can connect to dual cameras ranging from eight to 13 megapixels, and it has sufficient throughput to handle 1080p video at 60 FPS. A host of photographic features are included, including auto-exposure, auto-focus, auto-white balance, video stabilization, and a burst shooting mode.
That’s about it for the SoC’s north complex. The lower portion of the diagram above covers the south complex, which handles all sorts of lower-bandwidth I/O. In our briefing, Bay Trail’s chief architect, Rajesh Patel, wasn’t willing to divulge too many details about the nature of the switching fabric that connects the south complex to the system agent. We strongly suspect it’s the same Intel Optimized Switching Fabric, or IOSF, used in Avoton. IOSF is software-compatible with PCI Express, and it’s employed in Haswell and all of Intel’s current discrete platform controller hubs.
This interconnect is noteworthy because it’s an Intel-specific standard that allows the re-use of various logic blocks across a range of chip designs—and because it signals a move within Intel toward the SoC-style methods used to create many ARM-based chips. We learned in our Avoton briefing that “everything being developed now” at Intel makes use of IOSF.
Overview of the Bay Trail platform’s connectivity. Source: Intel.
The south complex offers links to a bunch of tablet- and PC-style interfaces. The biggest highlight may be the inclusion of USB 3.0 for truly speedy external connections. Bay Trail supports the USB “On-The-Go” spec, as well, so systems based on it should be able to act either as hosts (to devices like iPods) or as clients (to desktop PCs and the like.) Conspicuous by their absence are external PCI Express lanes and SATA ports. Primary storage will have to be handled by the eMMC interface, instead.
Of course, as a tablet chip, Bay Trail makes extensive use of the latest power-management techniques. Both the CPU and graphics cores can scale their clock frequencies and operating voltages in response to varying workloads. In addition, the chip can share its power budget between its major components, allowing additional performance headroom in certain cases.
For example, the image above cycles through several potential scenarios where individual CPU cores or other portions of the chip aren’t in use. These units are powered down, freeing up thermal headroom. In response, the still-busy CPU cores or integrated graphics can temporarily exceed their usual clock speeds.
Oddly, Intel calls this “Burst Technology,” rather than Turbo Boost, in the context of the Atom. The branding is kept separate because the Turbo tech in the Core processor lineup is still more advanced, with a broader dynamic operating range.
Many of the big components of the SoC are in their own power islands, with separate voltage supply rails, power gates to shut off inactive areas, or both. The illustration above offers a quick glimpse of Bay Trail’s dynamic power management in action via thermal imaging. In one case, only two cores appear to be active. In the next, all four CPU cores are active. In another, they all look to be powered down.
The final shot shows an almost completely dark chip.That’s presumably one of Bay Trail’s idle states. Like Haswell, this SoC pursues power savings, even between keystrokes, by dropping into a series of “active idle” states known as S0ix. These power states are managed in hardware and should be transparent to software and the OS. The deeper the sleep, the longer it takes for the chip to wake up. Intel’s Rajesh Patel again wouldn’t offer too many details about S0ix behavior in Bay Trail, but we’d expect much more aggressive pursuit of deeper idle states than in Avoton.
The Atom Z3000 series
Intel is spinning Bay Trail into five different models that make up the Atom Z3000 series, as shown below. These chips have been sampling for months now, as I understand it, and Intel anticipates that products based on them will be available for the holiday season.
The Atom Z3000 series will occupy tablets and convertible systems with screen sizes ranging from 7″ to 11″ and prices up to about $599. There may be some overlap, but generally speaking, systems costing more than that will likely be based on Haswell rather than Bay Trail. Intel estimates that it has 30 different design wins for the Atom 3000 series at present, and it expects that list to grow.
The Atom Z3000 series. Source: Intel.
The Z3000 series will support both the Windows 8.1 and Android operating systems at launch, but the Windows 8.1 situation is a bit tricky. Initially, only the 32-bit version of Win8.1 will be fully supported with connected standby capability, a crucial feature for tablets. Intel has pledged to deliver full 64-bit support with connected standby in the first quarter of next year. Apparently, the hold-up is software; the company claims the hardware is ready.
Obviously, the initial lack of 64-bit support isn’t a deal-breaker in tablets, since the scads of Android and iOS-based tablets in the market are 32-bit devices. Still, being stuck with 3.5GB of usable memory in Windows isn’t ideal, especially for convertible devices that dock with a keyboard and should be more than capable of serious productivity work. The delay in 64-bit support at least mitigates one of the advantages of going with a Wintel device over something else.
I’d like to show you the power specifications of these new Atoms, but Intel has decided not to be too specific on that front. Because of all of the dynamic power management at work, there’s some dispute over the proper power metric for this class of chip. (Intel has two specs, TDP and SDP, that it uses in different contexts.) We will talk a little bit about measured power use shortly, though.
In addition to the Atom Z3000 lineup, Intel will offer Bay Trail chips for traditional notebooks and desktops under the Pentium and Celeron brands. In fact, Intel’s NUC group has Bay Trail-based systems on its roadmap.
We visited Intel’s offices in Santa Clara, California for a first crack at testing Bay Trail’s performance. Although we’re happy to have the chance to test and relay some initial performance information to you, please understand that the information you’re about to see isn’t quite like what you might normally find in one of our reviews.
Although Intel was willing to let us run any test we wished, we were faced with a number of practical constraints, including very limited testing time and a spotty Internet connection. Some of the comparative results you’ll see below come from 64-bit executables in Windows 8, while the Bay Trail tablet we tested was running the 32-bit version of Windows 8.1 and could therefore run only 32-bit executables. We were faced with different OS versions on Android, as well. Some of our cross-platform, browser-based benchmarks are as influenced by the performance of the web browser software as they are by CPU speed, and we weren’t able to use the same browser and revision everywhere, although we did try to stick to Chrome 27.0.1453.94 in Windows.
That said, we think the performance results below ought to be sufficient to give you a general sense of Bay Trail’s competitive standing. Just be aware that the data aren’t as neat and clean as what we’d put into graph form most of the time. We’ll want to follow up with testing of production Bay Trail tablets in our our labs at a later date—and probably with better, more user-experience-focused benchmarks, as well.
Here’s a look at the Bay Trail tablet we used for testing. This is an Intel reference design for 10″ tablets, not something intended for production in exactly this form. The system has an Atom Z3770 processor inside, with clock speeds up to 2.4GHz with Burst. It also has 2GB of DDR3L-1066 memory. The display is ridiculously sumptuous, packing a 2560×1440 array of pixels into a 10″ diagonal rectangle. I stared.
The tablet is fanless and similar in size, thickness, and weight to the current iPad. We used two of these test systems, one running Windows 8.1 32-bit and another running Android 4.2.2. The Win8.1 tablet was in pretty good shape for a pre-release device. We noticed a few quirks here and there, but it generally animated that near-four-megapixel display fluidly. The Android-based systems were more obviously in an early, pre-production state. They had some issues with touch responsiveness and the like, and Intel was very candid about the need for additional tuning before Bay Trail-based Android systems are ready for the market.
Quite honestly, I’d like to spend more time with one of these systems before offering a strong assessment of the general user experience. What I saw of them was good, but obviously marred by little hiccups here and there that wouldn’t likely be an issue in a final, shipping product. I can say that a number of casual games and even some lightweight 3D games in Windows, like Torchlight 2, appear to run well on the Bay Trail reference tablet. That fact is vaguely amazing given where even full-sized Intel laptops were several years ago.
First up is a pair of brower-based benchmarks that, with some caveats about software influencing performance, we can run across a host of different OSes.
As you can see, Bay Trail gets off to a very solid start, nearly cutting execution times in half compared to the prior-gen Clover Trail Atom Z2760. It outperforms all of the ARM-compatible SoCs we tested, including those based on alternative CPU architectures like Krait and Swift.
Also intriguing is the match-up between Bay Trail and the AMD “Kabini” A4-5000 SoC, which has four Jaguar cores clocked at 1.5GHz. The A4-5000 SoC alone has a TDP rating of 15W; we’d expect max power draw on an entire Bay Trail platform to be lower than that. Yet the Atom Z3770 prevails, with a slight performance edge over the Kabini-based laptop in both tests.
In these Windows-only applications, Bay Trail achieves something close to three times the CPU performance of Clover Trail overall. The new Atom SoC even challenges the low-end Ivy Bridge dual-core, the Core i3-3217U, in several cases. (It’s much faster in AES encryption because Intel has disabled the Core i3’s AES-NI support for product segmentation reasons.)
The new Atom’s performance continues to match or exceed the AMD A4-5000’s, as well.
In Cinebench, our most floating-point intensive test, Bay Trail more than doubles the single-threaded performance of its Clover Trail predecessor. The new Atom’s per thread performance is also about half that of the Core i3-3217U—and remember, the Core i3 is a 17W chip with even higher total platform power draw. The Silvermont microarchitecture is putting in a tremendous showing.
Here’s an Android-only graphics test that gives Bay Trail a chance to square off against Nvidia’s Tegra 3 and Qualcomm’s Snapdragon. What you need to know in order to understand these results is simple: both the Transformer Infinity and the Nexus 7 have 1920×1200 display resolutions, and they’re running the test at that native res. The Bay Trail tablet is pushing 60% more pixels, at 2560×1440, yet it’s still hitting the frame rate you see.
Now, a caveat: I’m pretty sure both the Nexus 7 and the Bay Trail system are hitting a vsync cap, limiting them to about 60 FPS, so we can’t say too much about how they truly compare. Ah, Android…
The first set of 3DMark Ice Storm scores is just chaotic. I didn’t lower the resolution on the Bay Trail tablet to match anything else, and I believe this test just runs at the native display resolution. Despite the handicap of having to push twice as many pixels as anything else, at least, the Bay Trail SoC scores reasonably well.
The “Unlimited” test is more what you want. It renders to a 720p off-screen buffer, providing a true cross-device comparison of performance. Unfortunately, this test is only built into the brand-new revision of 3DMark, which wasn’t yet out for Windows when we tested. In this much better comparison, the Atom Z3770 proves to be substantially faster than the Nexus 7 and the iPad 4.
We didn’t have nearly enough time to conduct battery life testing. However, we were able to measure the power consumption of a couple of tablets—one based on Clover Trail and the other on Bay Trail—at the battery connect point.
What we saw was very similar power consumption from one generation to the next. Both tablets tended to idle at about 2 W of power draw, and both used 3-4 W during video playback. Total system power draw is probably a bit higher during CPU- and GPU-intensive workloads, but we didn’t get any full-platform power use numbers for such scenarios.
We also got a look at the individual power consumption of our tablets’ graphics and CPU components in two scenarios: gaming and SunSpider testing.
While gaming, the Clover Trail system’s graphics drew about 650 mW, and the CPU drew 700 mW. The Bay Trail system’s total power use wasn’t far from Clover Trail’s, but the mix was very different, with 1.2W going to the IGP and 100-150 mW heading to the CPU. To be fair, though, the Bay Trail IGP was driving a much higher-resolution display.
In SunSpider, the CPU/GPU split on Clover Trail was 900/350 mW, while Bay Trail’s was 1000/475 mW—again, comparable total power use. Of course, Bay Trail finished the SunSpider test in half the time and then dropped back to idle, so it was easily the more power-efficient solution overall.
I think the big takeaway here is that Bay Trail’s power consumption habits should make it suitable for eight-hour-plus battery run times in tablets, much like Clover Trail before it. The big change is that you’ll be getting substantially higher performance at the same time.
The results we’ve shown you are admittedly early indicators, but they all seem to point to the same conclusion: that Intel has brought its considerable resources to bear on the tablet SoC market and delivered a best-in-class solution. The Silvermont CPU microarchitecture is a huge step up in per-thread performance, which is just what the Atom has needed for a while now. Bay Trail’s graphics are substantially better, too.
The question now is whether Bay Trail can find its way into the hands of consumers in really large numbers, which is the true measure of success for any consumer-focused SoC. For that to happen, Intel doesn’t just need to collect lots of design wins in various tablets and convertibles. Bay Trail has to ship inside of systems that are really good, the sort that can be truly popular with consumers. Whether that’s more likely to happen with devices based on Android or Windows 8.1 is tough to say. Windows-based convertibles still seem to have tremendous promise, and Bay Trail should allow for the creation of some compelling systems. But Microsoft has barely put a dent in the tablet market so far. Android may be the better opportunity.
At any rate, Intel certainly seems to be doing its part; its tablet SoC offering has made major strides from one generation to the next.