A look at VIA’s next-gen Isaiah x86 CPU architecture

A brand-new x86 processor microarchitecture doesn’t come along every day, but today, we have just that. We visited the offices of VIA Technologies’ processor subsidiary, Centaur Technology, Inc., yesterday to learn about its new x86-compatible processor architecture. Remarkably, Centaur President Glenn Henry and his team of less than 100 people have created a thoroughly modern x86 processor microarchitecture from scratch over the course of the last four years. The resulting design, which bore the code-named CN during its development and is also known as the VIA Isaiah microarchitecture, is a superscalar 64-bit processor with speculative, out-of-order execution.

As a new design, Isaiah’s overall set of capabilities and features reads more like Intel’s Core microarchitecture than anything else, but Centaur has aimed Isaiah at the same set of targets its C7 and prior CPUs have sought. That means low power consumption and low cost come first, with performance taking a back seat. Yet by moving from the C7’s simple, in-order architecture to a brand-new core with speculative, out-of-order execution, Centaur has the potential to deliver quite a bit more performance within its chosen set of constraints. Henry says the firm set the goal of delivering twice the C7’s performance at the same clock speed and within the same power envelope. VIA now claims Isaiah has two to four times the C7’s per-clock throughput, depending on the application.

That order of performance gain—achieved by what Henry described as “real man’s architecture” rather than process technology optimizations or a move to multiple cores—may sound promising, but Centaur is careful about setting expectations for the performance of Isaiah-based processors. The first implementations will be single-core chips topping out at around 2GHz, mainly intended for embedded applications, ultra-mobile PCs, very low cost desktop PCs, and so-called mobile Internet devices. Isaiah’s mission is to add new capabilities and new instruction sets—like x86-64, SSE3 and virtualization extensions compatible with Intel’s VM provisions—in order to enable such devices to run newer applications competently.


Centaur’s Glenn Henry expounds on Isaiah.

Centaur isn’t shy about taking on the competition in the markets it serves, though. In our meeting, Henry stated flatly that, based on what little we know about it, Intel’s Silverthorne processor won’t be as fast as Isaiah since it’s an in-order design. He observed with seeming bemusement that Intel was developing an in-order architecture for this market just as Centaur was moving to an out-of-order design.

Regardless of its target market, the Isaiah microarchitecture’s feature set impresses. Henry has authored a reasonably accessible architecture brief on Isaiah, even (quite comically) mapping Isaiah microarchitectural features to Intel marketing names like “Wide Dynamic Execution” in a series of footnotes. This brief reveals almost everything VIA has chosen to disclose about Isaiah to date, and I’d encourage reading it if you want the full scoop on this architecture. We will, however, discuss some of the highlights of the design. Here’s a quick logical overview of Isaiah:


A logical diagram of the Isaiah architecture. Source: VIA.

From this altitude, Isaiah looks very much like any modern x86 processor. Isaiah can decode three x86 instructions per cycle, which it translates into micro-ops for internal execution. Like Intel’s Core, Isaiah can fuse multiple micro-ops into one, and it can combine multiple x86 instructions (like a compare-jump pair) into a single micro-op.

The chip can then issue as many as seven micro-ops per cycle to its seven execution ports. Those ports include two ALU ports for integer math, what Centaur calls a store address port and a store data port, one load port, and two media ports. The first media port is 128 bits wide and handles floating-point addition, SIMD integer operations, and divides and square roots. The second media port handles both integer and floating-point multiplication. According to Henry, “single-precision multiplies are fully pipelined with a world-record latency of three clocks.” Another interesting touch: this unit has a combined multiply-add capability used by more complex x86 instructions like transcendentals that are handled via Isaiah’s microcode subsystem.

Micro-ops are executed out of program order, and they’re then retired in program order at a rate of up to three per clock, which equates to as many as three x86 instructions.

Isaiah also features new and distinctive multi-stage branch prediction logic and a “memory disambiguation” capability similar to the Core microarchitecture that can moves loads ahead of stores if there are no dependencies.


What’s where on the first Isaiah chip. Source: VIA.

Isaiah’s cache subsystem looks to make the most of its likely modest overall size with uncommon smarts. Isaiah’s L1 instruction and data caches are both 64KB in size and 16-way set associative. The L2 cache is similarly 16-way associative, and initial implementations will be 1MB in size, although Henry indicated that different L2 sizes are a distinct possibility. The L2 cache is exclusive, so it doesn’t duplicate the content of the L1 caches, effectively raising the total capacity of the cache hierarchy. Like other current CPUs, Isaiah uses predictive algorithms to examine data access patterns and prefetch some data directly into its L1 cache, but uniquely, it prefetches data less likely to be used into a smaller, dedicated buffer rather than the L2 cache.

Centaur sounds positive about the performance prospects of the first Isaiah-based chips, but Henry said they’re “infinitely smarter” as a result of having the first real chips back from the fab. The team is now able to watch what’s happening inside the chip as it operates in a way they could not during simulation, allowing them to make smarter decisions about things like queue depths and buffer sizing. Centaur is currently working on tuning the architecture and expects to achieve performance gains in future Isaiah-based products. New architectures do tend to afford opportunities for optimization; even Intel saw some nice performance gains when moving from Merom to Penryn.

Power, not performance, is the key

Even so, Isaiah isn’t likely to rival Core for outright or clock-for-clock performance. Henry proudly noted that Isaiah’s execution units have some strong points, such as low latency for an FP add or multiply. But Isaiah has fewer integer ALUs and fewer multipliers than Core, and Intel “can push more instructions through” its machine. Much of this difference is attributable to Centaur’s radically different design philosophy, centered around both more limited resources and very different goals. Henry noted that, at a high level, Isaiah looks like any other out-of-order machine. One level below that, however, he said Centaur has made thousands of choices that are quite different from those that an Intel or an AMD would make.

Many of those choices are aimed at conserving power. For instance, Henry said Centaur’s designers used a number of circuit design techniques to keep power consumption low, such as avoiding using the smallest possible feature sizes available to them on the 65nm process node in order to avoid leakage problems. Some areas of the chip are actually larger than they’d otherwise have to be if power efficiency were not such a priority.

Centaur has outfitted Isaiah with a range of power-saving technologies, including a dynamic clock scaling mechanism similar to Intel’s SpeedStep that alternates between a pair of PLLs to achieve very quick multiplier transitions. The chip’s adaptive thermal mechanism will modulate voltage based on die temperature, taking advantage of better conditions to keep voltage low or even overclocking the processor if the thermal and voltage headroom is available. Isaiah’s complement of power states includes a new C5 sleep state in which the chip flushes caches and powers them down, and Henry said a future stepping of the chip will introduce a new C6 sleep mode. In C6, the processor will save its state into internal memory that’s powered by I/O voltage, and then the system can literally turn off VCC to the part, which should make for an ultra-low-power sleep state.

Small, cool, and competent

Despite all of the changes, Isaiah processors remain bus- and pin-compatible with VIA’s current C7 processors, and they fit within the same thermal envelopes, so they should be easy upgrades for companies that manufacture C7-based products. The first Isaiah is a larger chip than the C7, as illustrated by the picture below, which shows several Isaiah chips next to a single C7.


Four Isaiahs (left) next to single C7 (right). Forgive the flaky focus.

As with the C7, Isaiahs will largely ship soldered to the motherboard, not in a socket. The chips’ BGA-style package measures only 11 mm by 11 mm.

C7 chips are manufactured on a 90nm process, while Isaiah will begin life at 65nm. VIA wasn’t especially keen on revealing the name of the foundry that produces the chips, but I couldn’t help noticing the “Fujistu 65nm” label printed on a sign next to a diagram of the Isaiah processor in Centaur’s offices. Henry estimates Isaiah’s transistor count at 94 million, versus 25 million in the C7, but he sensibly insists the number is meaningless because it’s dominated by Isaiah’s larger 1MB L2 cache.

VIA expects Isaiah-based processors to begin shipping in the middle of 2008. Even after that happens, the C7 will continue as a lower cost option in its product portfolio.

We weren’t able to run any benchmarks, but Centaur did have several demo systems set up in order to show off its new processor’s capabilities. One of them played back a compressed video at 720p resolution using the combination of a 1.2GHz ultra-low-voltage Isaiah chip and a VX800 chipset connected by an 800MHz front-side bus. This system used only passive cooling. Another demo rig played a Blu-ray disc fluidly using a 1.3GHz Isaiah assisted by a Radeon HD 3850. And the third system combined a 2GHz Isaiah with a GeForce 7950 GT to run a couple of games, including Viva Pinata and Crysis. I wasn’t able to play any games on this system in our limited time there, but they did look to run smoothly enough.

These demos of basic competency in common tasks jibe with the zen of Centaur’s approach to processor development, which is very much about just being good enough. Henry will patiently and persuasively lecture anyone who will listen about his philosophy. As you listen, you realize you’re hearing the voice of the radical commoditization of x86 processors. He points out that most people don’t and shouldn’t care what type of CPU they have in their PCs, so long as it gets the job done. When Centaur started, Henry says, they had to develop engineers with a different mindset, not “faster is better.” He set a series of targets involving die size limits and a ship date, and then directed his people to make the processor fast enough within those constraints that people would want to buy it.

This approach sounded quite foreign to many of us when Centaur first began, but with the advent of devices like the Eee PC, the iPhone, and Shuttle’s kPC, it no longer seems so strange. Indeed, once you’ve absorbed the Centaur mindset, Henry’s answers to questions become somewhat predictable. Will Isaiah go multi-core? It can; it’s built that way, and Henry thinks Intel’s approach of a shared L2 cache makes sense. But he scoffs at the notion that people need multiple cores in basic computing devices right now. Henry says Centaur will go to multiple cores if it needs that level of performance or if Intel convinces people they have to have it.

Some portion of the x86 processor market will be receptive to Centaur’s low-cost, low-power proposition, and I suspect that portion of the market will grow substantially in the coming years. Whatever happens, I must admit that the low-cost, low-power, make-it-adequate pitch sounds much better when served alongside a modern 64-bit superscalar, out-of-order CPU architecture like Isaiah.

Comments closed
    • pogsnet
    • 12 years ago
    • Bensam123
    • 12 years ago

    Problem with Henry’s view on microprocessers is he’s building for what is required now and what people /[

    • Hattig
    • 12 years ago

    If the motherboards with this CPU on it are priced right, then I’m definitely interested in building a silent HTPC system around it.

    Also here’s hoping that a future EeePC or similar will be using this chip.

    At 60mm^2 the 65nm die is nearly twice the area of the 90nm C7, but 60mm^2 is still very small (smaller than the 130nm C3 IIRC). VIA will be getting loads off of a 12 inch wafer, so there’s hope that the price will be good.

    I got an EPIA800 motherboard / system around 5 years ago. It was very neat, although not the best CPU power in the world. The insane thing is that the price of the components has hardly dropped since then – newer boards just cost more and more and more. Hmm, actually the EPIA-ML8000 costs more than the EPIA800 did back in the day, despite the exchange rate changing so much the price should be even lower.

    • Stranger
    • 12 years ago

    I was wondering if via would bite the bullet and stuff everything into one die.

    I wonder who the first manufacturer will be who stuffs 1 core a small graphics core, a 64 bit memory controller and a link that would attach to a SB that would deal with all the IO/ pad intensive stuff.

    ps when did the front page BB become case sensitive for the Name field?

      • Dirge
      • 12 years ago

      I noticed the case sensitivity too. It’s a bit of a pain.

      • swaaye
      • 12 years ago

      MediaGX! oh noes! Not again!

        • Forge
        • 12 years ago

        That and the cancelled Tejas Celerons.

    • Hattig
    • 12 years ago

    l[

    • tfp
    • 12 years ago

    I’m sure this will never happen but I wouldn’t mind a 478 socket compatible version of these. If the performance is ok it would be a nice way to turn an older power hungry machine into a power sipping machine.

    • pogsnet
    • 12 years ago
    • Forge
    • 12 years ago

    I want one of these in an EEE v2 with an 8-16GB SSD and a larger screen. That would be really sweet for mobile movies.

    • Shinare
    • 12 years ago

    I would love to see a pico-itx with that 2GHz and a DVI or HDMI out on it. That and a small SSHD would make a nice little computer for internet/pictures/blu-ray on your TV.

    • swaaye
    • 12 years ago

    Heh. I wonder if this little guy rivals a single Phenom core clock-for-clock. I wouldn’t be surprised if it did. 🙂

    Long live the Winchip 2! (it was sorta neat!)

      • seeker010
      • 12 years ago

      Well if true, that would really spell trouble for AMD, to lose to the tiny Isiah core from scrappy Via.

      • stmok
      • 12 years ago

      Not likely, but I suspect the performance gap is gonna be much closer than the current C7 was.

        • swaaye
        • 12 years ago

        C7 performed like a Tualatin or Willamette on RDRAM per-clock. Not bad for what C7 is and what those other cores are, I’d say. I wouldn’t be all that surprised to see this thing match a Phenom core, considering a Phenom core is sometimes slower than an Athlon 64 core. Clock speed will obviously keep them far apart though.

    • Kent_dieGo
    • 12 years ago

    This would be perfect for a small passivly cooled home theater PC. I hope they have some sort of speed reduction power saving scheme like C-n-C or SpeedStep to make having one of these on next to the TV practical.

      • eitje
      • 12 years ago

      the EPIA boards that VIA currently sells are already good enough for a passively-cooled HTPC. check ’em out. 🙂

      • stmok
      • 12 years ago

      The CN has some interesting power saving features. I suggest you go read up on them

    • Crayon Shin Chan
    • 12 years ago

    Hey, those guys are still alive, thank lord. What ever happened to Intel threatening to take its x86 license away? I remember it had something to do with a rock and a hard place.

      • Furen
      • 12 years ago

      As far as I know, Intel was threatening to remove their front-side bus license and was demanding that they withdraw from the CPU market in order to retain it. As far as I know, Centaur and IDT have x86 licenses similar to AMD’s (gained through court judgements). I doubt VIA has much of a future in the core-logic market so I think agreeing to Intel’s terms would have been a death sentence.

      • stmok
      • 12 years ago

      The Intel cross-license agreement with VIA, as I recall, was to do with the P4 bus and NOT to do with x86 processors. The agreement was to allow VIA to be licensed the use of the P4 bus in their chipsets.

      Intel chose not to extend this agreement, and so it ended in March 31, 2006.

      VIA took the initiative and made their own called the V4 bus.

      So they’ll still produce chipsets for Intel processors. Although, I’m not sure if there’s a big performance hit from using a VIA with V4 bus compared to an Intel one.

      At this time, I know the VIA C7 and the recently discussed CN or Isaiah processors, uses the VIA V4 bus.

    • Nitrodist
    • 12 years ago

    I’d really like to see VIA get into large scale x86 processing, such as C2D’s or the Athlon’s. It’d be interesting to see what kind of improvements they can achieve with a larger power envelope and larger die size.

      • eitje
      • 12 years ago

      i don’t think they’d do a very good job.

      this is like wondering how well a champion marathon runner (or any athlete from a sport where energy conservation is brutally required) would do in a sprint.

      they’re specialists at getting the most output from the least energy input. they should keep doing that. 🙂

        • Nitrodist
        • 12 years ago

        Well, likewise, should Intel (the sprinter) be going into VIA’s arena (marathons)?

          • eitje
          • 12 years ago

          i think they hired on an entirely new team to do the marathon. 🙂

    • MarioJP
    • 12 years ago

    Just when you thought that the PC market can’t get any worst than it is already in. now a third player in the cpu arena??. Great now thats just going to really kill off PC gaming. Its hard enough as it is trying to stay afloat. Why add more fuel to the fire?

      • echo_seven
      • 12 years ago

      I don’t understand, why is VIA joining the fray a bad thing? I would have thought its a good thing, making Intel really work(by giving us good CPUs) for our money…

      and why does this affect PC gaming???

      • LoneWolf15
      • 12 years ago

      And your post is relevant how? We aren’t even TALKING gaming here.

      This is about low-power computing devices. When has gaming EVER been about low-power? Never.

      As for your comment about a third player being worse, obviously you don’t understand that competition is a good thing in business and technology. It stops any one company from resting on its laurels too long, and forces them to innovate or die. Example: Without AMD being around, we might well still be stuck with the P4/Netburst architecture, a world of relative poor performance and high power consumption. AMD’s innovations pushed Intel to do some of its best work ever with Merom/Conroe/Penryn.

      In the same vein, VIA is a company that will push Intel to do better than Silverthorne. Your post makes absolutely no sense whatsoever, both in being out-of-context, and in failing to explain your reasoning of why ANY of this would kill gaming or the PC market.

      • maxxcool
      • 12 years ago

      Via / Centaur has been around forever, thee not “joining” the fray so to speak they have simply been on the sidelines. they never tried to be a gaming CPU either…..

      • stmok
      • 12 years ago

      If you really have nothing constructive to say…Don’t say a thing.

    • TurtlePerson2
    • 12 years ago

    Very well done article. I’ve read a couple of articles on this story and this one is by far the best.

    Personally, I find the idea of doubling performance for the same power draw and heat more exciting than what’s happening on desktops right now. CPUs are taking more and more juice to run and improvements are all too often coming in number of cores rather than power per core.

    I can see these processors going everywhere. If they have a low power chip that works really well, they can probably make a high power chip that runs much faster. I’m curios to see if they expand into the laptop or desktop market with this chip.

      • Nitrodist
      • 12 years ago

      Ahem, need I remind you of the P4 generation of chips? If anything, they’ve made leaps and bounds towards better power management.

    • mattthemuppet
    • 12 years ago

    That’s pretty neat, interesting read too. I’ve always thought that for the majority of tasks for the majority of people, current dual-core CPUs well exceed what is neccessary.

    On top of the usual comparisons (seemingly required to give C7=500MHz P3 type comment) it’d be interesting to see how these chips compared to current dual cores before higher P states kick in i.e. can a Core2Duo at idle (1.6GHz in most cases) crunch through a bench in the same time as an Isiah CPU at load.

    • tfp
    • 12 years ago

    The benchmarks will be interesting. I would like to see them and how it would do vs some of the old chips that might still be out and about. Along with benchmarks for newer lower end systems.

    • eitje
    • 12 years ago

    I can’t tell you how in love I am with VIA & Centaur products. They are so engineering-awesome!

    Scott, if you’re still in Austin, you should check out Kerbey Lane Cafe (breakfast foods, plus awesome queso), Maudie’s Cafe (Mexican), & Rudy’s BBQ (…BBQ!).

    I would also be glad to buy you a beer somewhere (Gingerman)! 😀

      • Dirge
      • 12 years ago

      I like the idea of a passively cooled computer and I like what VIA/Centaur have been doing in this avenue. Hopefully the performance matches what Centaur are hinting at.

    • Furen
    • 12 years ago

    It would have been nice if the article mentioned the TDP targets for the 1.2GHz ULV and 2.0GHz parts, mostly because Centaur puts so much emphasis on TDP. It’s kind of funny that they used a 3850 to assist in the bluray decoding test since we all know AMD’s 3000 series (and Nvidia’s 8000, for the most part) can pretty much offload all this off the CPU. That said, I’m sure Isaiah will be a good match for the 3450 in low-power, small-form-factor systems.

    I must say that I do find this architecture a bit exciting since since it could lead to some interesting ultraportable laptop designs… think Asus’ Eee with a faster CPU without increasing power draw much, if at all.

    #4, Well, he DID say “basic” computing devices. Hell, I think ultraportable laptops can get away with single-core, too, unless they’re used as your primary computer.

      • Damage
      • 12 years ago

      We had limited time and didn’t get into specifics on this front beyond “same as C7.” The C7 tops out at 20W for the 2GHz part, which is peak (TDP). They have a 3.5W ULV part, as I understand it, and Henry told me they’d have a 3.5W Isaiah, as well.

    • Sargent Duck
    • 12 years ago

    /[

      • A_Pickle
      • 12 years ago

      Plus it moves the industry. Multi-core does give you more resources, and as soon as the software comes out to take advantage of that… well… that’s when “Intel convincing people they need it” shows it’s better side.

      And, seriously — when a multi-core processor can be had for under $100? Are you kidding me?

        • ew
        • 12 years ago

        Buying two computers also give you more resources. What exactly is your point? If a single core computer satisfies the needs of most people why should they waste even a penny more on something they don’t need?

      • Anonymous Coward
      • 12 years ago

      Allow me to suggest that some reason other than the lack of a core is what makes your mom’s machine painful. I’ve used SMP machines as my primary desktops for maybe 7 years now, but I’ll take a pile of RAM over a second core any day.

        • LoneWolf15
        • 12 years ago

        Hear Hear! While my primary system is dual-core, I’ve got plenty of single-core machines at home and at work that are plenty fast for almost every task out there. Remove other bottlenecks (e.g., have enough RAM, have a fast hard disk with a decent cache, use even a basic discrete video card) and a single-core CPU will do almost everyone’s day-to-day tasks fine.

        When I find someone has a slow system, it almost always boils down to one of the following factors:
        –Malware/Spyware
        –Not enough RAM
        –a really slow hard disk (or one starting to fail)

        I’ve never seen it come down to being “just a single-core processor”. Unless you’re running Maya or LightWave on your mom’s computer, that is.

    • crazybus
    • 12 years ago

    Wow, I’m actually interested in a VIA cpu. Good stuff. Hopefully they’ll be able to ship silicon in a reasonable amount of time.

    • flip-mode
    • 12 years ago

    Very cool article. Thanks Scott. I’m anxious to see how these CPUs are put to use.

      • ssidbroadcast
      • 12 years ago

      I’m thinking Kiosk, embedded-system applications.

        • flip-mode
        • 12 years ago

        what about print server, mail server, anti-virus server, license server stuff? The machines we have doing these things at work (less than 50 users) are all running less powerful CPUs (a few pentium machines, a pentium 3 machine).

          • UberGerbil
          • 12 years ago

          Point of sale machines represent a huge business, and many of them are still running sub-1GHx celeron-class processors.

          • ssidbroadcast
          • 12 years ago

          What the heck is an anti-virus server and a license server?

            • just brew it!
            • 12 years ago

            Some software licenses allow you to use up to some maximum number of copies simultaneously across an enterprise. You can have the software installed on many more machines than that, but only the licensed number of copies can actually be running at any given time. The license server runs a process that monitors how many copies of the licensed software are running on the LAN at any given moment.

            Solidworks (which a number of the engineers where I work use) is one example of an application which works this way.

            • Saribro
            • 12 years ago

            Maple 11 is set up that way at our campus too.

          • sroylance
          • 12 years ago

          Your workload would be better suited to virtualization. Buy one 2xquad core machine w/ 16GB of RAM and run all of those things, in their own OS, on the same hardware.

            • eitje
            • 12 years ago

            with the look of these procs, it might not be necessary to over-buy like that. a system based on this chip might be able to perform all of the functions flip mentioned, and without a fan to boot! 😀

    • UberGerbil
    • 12 years ago

    Good for them. That’s no small task.

    It’s going to be interesting seeing this go up against Silverthorne. Intel’s entrant my legitimize (and perhaps vastly expand) the product segment, but it looks like it will be at quite a different power/performance point. It will be an interesting segment indeed where VIA is the performance leader and Intel is the low-power champion.

      • Stranger
      • 12 years ago

      It seems like silverthrone is going for a different market. I was getting the impression that silverthrone was going for the embeded market while this will go for the super low end market.

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