The Current Intel offerings

Before we can discuss the ARM server SoCs, we want to look at what they are up against: the current low end Xeons. We have described the midrange Xeon E5s in great detail in earlier articles.

The Xeon E3-12xx v3 is nothing more than a Core i5/i7 "Haswell" dressed up as a server CPU: a quad-core die, 8MB L3 cache, and two DDR3 memory channels. You pay a small premium – a few tens of dollars – for enabling ECC and VT-d support. Motherboards for the Xeon E3 are also only a few tens of dollar more expensive than a typical desktop board, and prices are between the LGA-1150 and LGA-2011 enthusiast boards. The advantages are remote management courtesy of a BMC, mostly an Aspeed AST chip.

For the enthusiasts that are considering a Xeon E3, the server chip has also disadvantages over it's desktop siblings. First of all, the boards consume quite a bit more power while in sleep state: 4-6W instead of the typical <1W of the desktop boards. The reason is that server boards come with a BMC and that these boards are supposed to be running 24/7 and not sleeping. So less time is invested in reducing the power usage in sleep mode: for example the voltage regulators are chosen to live long. Also, these boards are much more picky when it comes to DIMMs and expansions cards meaning that users have to check the hardware compatibility lists for the motherboard itself.

Back to the server world, the main advantage of the Xeon E3 is the single-threaded performance. The Xeon E3-1280 v3 runs the Haswell cores at 3.6GHz base clock and can boost to 4GHz. There are also affordable LP (Low Power) 25W TDP versions available, e.g. the Xeon E3-1230L v3 (1.8GHz up to 2.8GHz ) and E3-1240L v3 (2GHz up to 3GHz). These chips seemed to be in very limited supply when they were announced and were very hard to find last year. Luckily, they have been available in greater quantities since Q2 2014. It also worth noting that the Xeon E3 needs a C220 chipset (C222/224/226) for SATA, USB, and Ethernet, which adds 0.7W (idle) to 4.1W (TDP).

The weak points are the limited memory channels (bandwidth), the fact that Xeon E3 server is limited to eight threads, and the very limited (for a server) 32GB RAM capacity (4 Slots x 8 DIMMs). Intelligent Memory or I'M is one of the vendors that is trying to change this. Unfortunately their 16GB DIMMs will only work with the Atom C2000, leading to the weird situation that the Atom C2000 supports more memory than the more powerful Xeon E3. We'll show you our test results of what this means soon.

The Atom C2000 is Intel's server SoC with a power envelope ranging from 6W (dual-core at 1.7GHz) to 20W (octal-core at 2.4GHz). USB 2.0, Ethernet, SATA3, SATA2 and the rest (IO APIC, UART, LPC) are all integrated on the die, together with four pairs of Silvermont Cores sharing 1MB L2 cache. The Silvermont architecture should process about 50% more instructions per clock cycle than previous Atoms due an improved branch prediction, the loop stream detector (like the LSD in Sandy Bridge) and out-of-order execution. However the Atom micro architecture is still a lot simpler than Haswell.

Silvermont has much smaller buffers (for example, the load buffer only has 10 entries, where Haswell has 72!), no memory disambiguation, it executes x86 instructions (and not RISC-like micro-ops), and it can process at the most two integer and two floating point instructions, with a maximum of two instructions per cycle sustained. The Haswell architecture can process and sustain up to five instructions with "ideal" software. AES-NI and SSE 4.2 instructions are available with the C2000, but AVX instructions are not.

The advantages of the Atom C2000 are the low power and high integration -- no additional chip is required. The disadvantages are the relatively low single-threaded performance and the fact that the power management is not as advanced as the Haswell architecture. Intel also wants a lot of money for this SoC: up to $171 for the Atom C2750. The combination of an Atom C2000 and the FCBGA11 motherboard can quickly surpass $300 which is pretty high compared to the Xeon E3.

ARM, Micro and Scale-out Servers The ARM Based Challengers: AppliedMicro
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  • jjj - Tuesday, December 16, 2014 - link

    If you look at phones and tabs ,we might be getting some rather big custom cores in 2015 and 2016. Apple and Nvidia already have that, ofc much smaller than Intel's core when adjusting for process (actually that's an assumption when it comes to Denver since don't think we've seen any die shots).
    Intel at the same time in consumer is pushing for more non-CPU/GPU compute units and low power and they might face a tough question about core size and even process (if they target low clocks, low power , or the opposite).Got to wonder if at some point they'll have to go for a big core just for server.Would make things even more interesting.
    Might not matter but Apple kinda has the perf for an ARM Macbook Air if they go quad. Not something worth doing for such low volume but doable when they go quad on all ipads or sooner if they launch a bigger ipad. Could be a trigger for others pushing more ARM based Chromebooks and beyond. That would set the stage for even bigger ARM cores.
    Also got the feeling Nintendo will go ARM in 2016 and not many reasons for Sony and M$ not to go that way if they ever make a new gen- just another market for bigger ARM cores, any significant revenue helps with dev costs so it matters.
  • CajunArson - Tuesday, December 16, 2014 - link

    1. The Core-m is widely derided as not being fast enough for the MacBook Air.
    2. The Core-m is easily twice as fast as the A8X in benchmarks that count... even Anandtech's own benchmarks show that. Furthermore, when you step away from web browsers and get to use the advanced features of the Core-m like AVX, that advantage jumps to about 8x faster in compute-heavy benchmarks like Linpack.
    3. Even the mythical A9 coming in 2015 is expected to have roughly a 20% performance boost over the A8x.
    4. Any real computer using an ARM chip would have to have a translation layer just like the old Rosetta to run the huge library of x86 software out there. Rosetta sort of worked because the Core 2 chips from Intel were *massively* faster than the PowerPC parts they replaced. Now you expect to run the translation overhead on an A9 chip that is slower -- by a large margin -- than the Core-m parts you've already derided as not being good enough?

    Yeah, I'm not holding my breath.
  • fjdulles - Tuesday, December 16, 2014 - link

    You may be right, but remember that ARM chips using the same power budget as Intel core i* will no doubt be clocked higher and perform that much better. Not sure if that will be competitive but it would be interesting to see.
  • wallysb01 - Tuesday, December 16, 2014 - link

    Only if you want a glorified tablet as a laptop. The software most people use in real work on laptops/desktops is not going to be ported over to ARM at an speed, even if ARMs could do that work reasonably well.
  • Kevin G - Wednesday, December 17, 2014 - link

    I'm under the impression that a good chunk has already been ported. MS Office for example is native ARM on Windows RT. Various Linux distributions have ARM ports completed with ARM based office and desktop software. The main thing missing are some big commercial applications like Photoshop etc.

    The server side of thing is similar with Linux and open software ports. MS is weirdly absent but I suspect that an ARM based version of Windows 2012/2014 is waiting of major hardware to be released. Much of the Windows base is already ported over to ARM due to Windows RT.
  • Kevin G - Wednesday, December 17, 2014 - link

    Indeed. Performance of ARM platforms once power constraints have been removed is a very open question. So far all the core designs in products have been used in mobile where SoC power consumption is less than 5 W. What a 100 W product would look is an open and very interesting question.
  • Ratman6161 - Wednesday, December 17, 2014 - link

    If they "use the same power budget as an Intel core i*" then what would be the point?
  • jjj - Tuesday, December 16, 2014 - link

    Ok you are focusing on the wrong thing but lets do that anyway.
    I have never claimed that Apple's own SoC would beat Intel's current SoCs, just that the perf would be enough if they go quad and obviously higher clocks.
    When you talk Core M you should remember that the price at launch was $281 so it's not good enough for anything.
    Anyway how about you compare a possible Apple SoC with a MacBook Air from 2011, lets face it the Air is a crap machine anyway , not much perf and TN panel for w/e ridiculous price it costs now and it's users are certainly not doing any heavy lifting with it.
    At the same time Apple's own 15- 20$ SoC would allow them a much cheaper machine and a presence in a price segment they never competed in, adding at least 5B of revenue per year (including cannibalization) and a share gain in PC of 2-3%.
    But then again the point was that there are a bunch of trends that could favor bigger ARM cores.
  • Morawka - Wednesday, December 17, 2014 - link

    it might cost them $20 for the A8X in fab cost, but the R&D for that chip is in the 10's of millions. Factor that in, to however many they ship, and it adds at least another $20 per chip
  • jospoortvliet - Wednesday, December 17, 2014 - link

    Even more obvious then that this would save them money by spreading out the fixed costs over more devices...

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