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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  • esterhasz - Thursday, December 18, 2014 - link

    But this is exactly why a wider array of machines based on their chips would make sense: the R&D cost is already spent anyways, since iPhone and iPad need chips, selling more units thus reduces R&D cost per unit. Economies of scale.

    I don't believe a MBA variant with ARM is down the road either, but the rumored iPad Pro could develop into something similar rather quickly.
  • OreoCookie - Tuesday, December 16, 2014 - link

    If you want to talk about ARM on the desktop, that's a whole other discussion, but one that most certainly needs to include price: if the price difference between a Broadwell-based Core M and a fictitious Apple A9X is $200~$230, then this changes the discussion completely. Two other factors are graphics performance (the Core M has »only« 1.3 billion transistors, the A8X ~2 billion, indicating that the mythical A9X may have faster graphics) and the fact that Apple controls the release schedule and can spec the SoC to meet its projected needs. To view this topic solely through the lens of CPU performance is myopic.
  • darkich - Friday, December 19, 2014 - link

    Your comparisons missed the picture spectacularly.
    A8X is a 20nm 2-4W TDP chip with a price that is probably around 70$.
    Top of the line Core M5Y70 is a 14nm 4.5 W TDP chip with a price of 270$.
    And it has a weaker GPU, btw. (raw performance). And it throttles massively, effectively giving only 50% of the benchmark performance.

    If you're going to compare that to an Apple chip, compare it to a 14nm A9X with custom derived PowerVR series 7 GPU,(scales up to 1,4 TFLOPS) vastly expanded memory controllers connected to a much faster RAM (compared to one in the iPad) upclocked to 2GHz, that are available at any time.
  • darkich - Friday, December 19, 2014 - link

    .. *with cores upclocked to about 2GHz
  • Flunk - Tuesday, December 16, 2014 - link

    Nintendo already sells ARM systems, the 3DS and the DS before it are both ARM-based. The PSVita is ARM too. I don't see an ARM Macbook Air anytime soon, they need a bigger and higher-clocking chip for that and it doesn't look like that's going to happen anytime soon.
  • Nintendo Maniac 64 - Tuesday, December 16, 2014 - link

    Even the Game Boy Advance used an ARM7 for its main CPU.
  • jjj - Tuesday, December 16, 2014 - link

    Obviously there are handhelds using ARM but the point was about bigger cores and clearly not handhelds.
  • DLoweinc - Tuesday, December 16, 2014 - link

    Don't quote Wikipedia, not suitable for this level of writing.
  • garbagedisposal - Tuesday, December 16, 2014 - link

    Says DLoweinc, master of knowledge and scholarly writing.
    In contrast to your childish and outdated opinion, Wikipedia is a perfectly valid source of information, go read about it and quit crying.
  • Daniel Egger - Tuesday, December 16, 2014 - link

    The problem really is the custom solutions can simply not compete with Intel on any level for general purpose computing (which the majority of applications are), not on performace/price, performance/power and not even on features/price.

    For instance I can see a huge market for sub-Xeon (or Atom C) performance at a corresponding price -> not going to happen because everyone is targeting > Xeon performance at ridiculous prices because they're expecting the margin to be there however there're simply to many compromises to be made by the buyers so that has to fail.

    Also I can see a huge demand for Atom C - Xeon performance at lower power consumption however no one seems to be really targetting this, all we get are Raspberry Pi's and a bit beefier but close from even Atom C. The new virtualisation techniques (Docker et al) opened a whole new can of possibilities for non-x86(_64) devices because virtualisation is suddenly possible and much more lightweight than ever before but no one seems to want to jump this opportunity.

    I'd really like to buy some affordable general purpose (BYOM/BYOS) hardware which has a little bit of oomph and takes little power which should be the powerful sides of any of the contenders but somehow all fail to deliver and I don't even see an attempt to change that.

    If I want mind-boggling performance at decent performance/price ratio with real virtualisation and 100% standard software compatibility there's no way around the high end Xeons (and maybe AMD iff they manage to get their asses back up) and none of the contenders is ever going to challenge that so they might as well stop trying.

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