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Intel's Atom Architecture: The Journey Begins

 by Anand Lal Shimpi on April 2, 2008 12:05 AM EST
46 Comments | Add A Comment
46 Comments

Lower Power than Centrino

(This page is taken from our earlier look at the Intel Atom architecture)

With mobile Penryn Intel introduced a new power state it calls C6. In the C6 power state the CPU is in a virtual reset state, and core voltage is very close to zero. The core clock, all of the PLLs, and caches are completely turned off. All of the state data is saved in a 10.5KB storage area, similar to mobile Penryn (but smaller since there's not as much state to save). Upon exiting C6 the processor's previous state is restored from this memory, called the C6 array. It takes around 100us to get out of C6, but the power savings are more than worth the effort - it's a similar approach of power for performance that we saw in the design of the original Pentium M processor.

Clock gating (sending the clock signal through a logic gate that can disable it on the fly, thus shutting off whatever the clock connects to) is an obvious aspect of Atom's design. All Intel processors use clock gating; Atom simply uses it more aggressively - the clock going to every "power zone" is gated, something that isn't the case in mobile Core 2. Each logic cluster (205 total) in Atom is referred to as a Functional Unit Block (FUB) and the entire chip uses what Intel calls a sea of FUB design. Each FUB is clock gated and can be disabled independently to optimize for power consumption. The cache in Atom is in its own FUB, which apparently isn't the case in mobile Core 2.


Keeping Silverthorne on life support, only 21 pins are necessary

Atom uses a split power plane; in its deepest sleep state (C6) the chip can shut off all but 21 pins which are driven by the 1.05V VRM. By having two separate power planes the chip can manage power on a more granular level. While it can't disable individual pins, it can disable large groups of them leaving only 21 active when things like the L2 cache and bus interface are powered down.

Intel mentioned that Atom will remain in its C6 sleep state 90% of the time. However, that figure is slightly misleading because it's only possible to remain in C6 when the CPU is completely idle. The 90% figure comes from taking into account a mobile device sitting in your pocket doing nothing most of the time. When in use, Atom won't be able to spend nearly that much time in C6.

Despite the implementation of a C6 power state, Atom will still lose to ARM based processors in both active and idle power. The active power disadvantage will be erased over the coming years as the microarchitecture evolves (and smaller manufacturing processes are implemented), while the idle power requires more of a platform approach. As we reported in our first Menlow/Silverthorne article:

"The idle power reduction will come through highly integrated platforms, like what we're describing with Moorestown. By getting rid of the PCI bus and replacing it with Intel's own custom low-power interface, Intel hopes to get idle power under control. The idea is that I/O ports will only be woken up when needed (similar to how the data lines on the Centrino FSB function), and what will result are platforms with multiple days of battery life when playing back music."

Poulsbo's Graphics: Full HD Decode and not Made by Intel Performance Expectations
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  • AssBall - Thursday, April 3, 2008 - link

    I was a little surprised at first but when I got thinking... I don't really know if my P35 northbridge is even a 90nm chip.

    - Why would Intel not want to use its old rock solid 130 process that it spent a ton of money on to build simpler parts than it was designed for. As long as their materials and equipment are working fine for a cheap enough 130 part and there is no dire market for lower power chipsets that fit in an ATX standard...

    - Intel's most recent strategy has been to design and manufacture their latest designs on solid existing tech before they shrink it.

    I'm also fairly certain that if this little CPU takes off they will have the 90-65 version of it with some simple refinements out in two shakes of a lamb's tail. I'm really surprised myself that they set it up with ddr2 support... but again its so cheap now, why not?

  • rmlarsen - Wednesday, April 2, 2008 - link

    It is articles like this that make me come back to Anandtech. Well written and researched and with the right level of detail. Keep up the good work!

  • Woodchuck2000 - Wednesday, April 2, 2008 - link

    One of the best I've seen on Anandtech for quite a while. I've been following this one quite closely and it's great to have such a detailed exposition all in one place.

    Do we have any news on the availability of this as a desktop part? I've been looking to construct an always-on server sitting in a cupboard somewhere, just to act as a file/print server and to do a little light database/web hosting for testing and developement. A 1.6GHz Atom would easily provide enough horsepower to accomplish that and with a notebook HDD, the whole thing should stay well under 10W load power consumption!

    I saw a photo of Silverthorne + Poulsbo on an Intel reference board built to a Mini-ITX form factor but couldn't find any details on whether they were planning to release it to the general public...

    Also any news on when we might expect benchmarks?

    Keep up the good work!

  • yyrkoon - Wednesday, April 2, 2008 - link

    You could probably do this now with the VIA pico ITX reference board.

    http://www.logicsupply.com/products/px10000g?refer...">http://www.logicsupply.com/products/px1...=&gc...

    Sorry for the long link . . . but I think power usage is somewhere around ~12W.

  • AnnonymousCoward - Friday, April 4, 2008 - link

    Try tinyurl.com

    Thanks for such a high quality article, Anand!

  • tfranzese - Wednesday, April 2, 2008 - link

    "These days, Intel manufacturers millions of Core 2 Duo processors each made up of 410 million transistors (over 130 times the transistor count of the original Pentium) in an area around 1/3 the size."

    ...is incorrect. You could nearly fit six Core 2 Duos at 45nm in the same area that the original Pentium occupied or even more impressive, four of them on the die of the original Pentium 4 with room to spare.

  • tfranzese - Wednesday, April 2, 2008 - link

    I'm the one with fuzzy logic today and misinterpreted :)

  • Magnus Dredd - Wednesday, April 2, 2008 - link

    It is completely true that there are benefits to having a single platform to support. However, the article is completely off the mark about where the benefits are most realized.

    It's not the HARDWARE.

    It's the API.

    It's all about the API. Unless you're writing drivers or an OS you're not writing to the hardware, with VERY few exceptions. The exceptions to this are for optimizations for seriously intense code like Photoshop filters and video game engines, where 90% or more of the code is to the API. So basically one way or another you're writing to an API. That's Application Programming Interface.

    Since it was mentioned in the article...

    If I'm writing a program that's supposed to run on OSX, the newest version supports TWO hardware platforms (PPC and x86, and not just x86 as the article claimed), and I want to create a "window" using the built in API (named Cocoa) I use the command NSWindow.
    http://developer.apple.com/documentation/Cocoa/Ref...">http://developer.apple.com/documentatio...SWindow_...
    It makes no difference when writing the program whether it's a PPC or Intel based machine that it will be running on with the single exception that in a few places you have to use a small bit of code to make sure that the program uses the byte order appropriate to the processor.

    While I have yet to read info on it, I'd bet that NSWindow is also used by the iPhone which uses a MIPS cpu (yet a third architecture).

    I've written code in ANSI C for Linux that runs without making any changes on PPC, x86(32 bit and 64 bit), and Sparc. If I wanted to go to the trouble I could also compile it on my MIPS based SGI, a Motorola 68000 series Mac, and a HP PA-RISC (if I can ever figure out how to get the damned thing running). That's because nearly all modern applications are compiled.
    ---
    Now if by PC, Anand meant Windows, we're talking a different story, but one with similar flaws.

    So I'm writing an application for Windows and I want to create a "window". I use the win32 command CreateWindow.
    http://msdn2.microsoft.com/en-us/library/ms632679(...">http://msdn2.microsoft.com/en-us/library/ms632679(...

    So lets just say that I want it to run on an Itanium under Windows... I use the win32 command CreateWindow.

    So let's just say that I want to make it run on a WindowsCE based set-top box or internet tablet powered by a MIPS CPU...
    I use the win32 command CreateWindow.
    http://msdn2.microsoft.com/en-us/library/ms908192....">http://msdn2.microsoft.com/en-us/library/ms908192....
    Quoting Wikipedia: "It is supported on Intel x86 and compatibles, MIPS, ARM, and Hitachi SuperH processors."
    http://en.wikipedia.org/w/index.php?title=Windows_...">http://en.wikipedia.org/w/index.php?title=Windows_...
    ---
    I'm actually somewhat saddened to write this post, mostly due to the the amount of respect I have for Anand and many of the great articles he's written over the years. However, I suppose that it goes that way sometimes.

    I just want to make sure that people aren't misled about what makes it hard to port/move a program to another platform like a phone or a BlueRay player. And it's sure as hell not the CPU's instruction set. The CPU may not be fast enough or it's that programs are written for these APIs that may or may not support the hardware. And the fault for this lies with Microsoft, or Apple, or the GTK guys, or Trolltech, or whomever the API belongs to.

    Also simply dropping an x86 CPU into a machine does not mean that it can run Windows. With the sales of XP to cease, your only option for the new batch of supercheap x86 laptops like the ASUS EEE, or the cloudbook may be Linux, regardless of the fact that it's x86 based.

    The bottom line is, if Microsoft doesn't care about your platform, they won't support it and you won't be able to get it with Windows regardless of what the CPU is.

    While I do personally agree that x86 moving "downwards" is a great thing. I just see it taking over for completely different reasons, like Intel's manufacturing prowess.

  • yyrkoon - Wednesday, April 2, 2008 - link

    Windows XP Embedded, and the compact .NET framework while you're talking about 'APIs', and platforms. XPe, and Win2003 Embedded are not going away any time soon, and basically have barely been available on a non beta basis. Although CE Builder could probably do the same thing, and as a matter of a fact I've seen some fairly nifty things done with it(eg: a boot-able image that fits on a floppy with all the functionality of your standard NAS, including User Groups and permission policies).

    While sometimes having an OS on an Embedded device may be a hindrance, there are times it can be quite handy. Bank KIOSKs, and Cash registers are only two such examples, and I have worked on/with both that use WinXPe.

  • Anand Lal Shimpi - Wednesday, April 2, 2008 - link

    Agreed - the API also plays a large part, but for a company like Apple the pain of maintaining both PPC and x86 codepaths is significant. Perhaps the Firefox reference wasn't the best one, especially as I really see the strengths here for software companies like Apple (not to mention what other conventional hardware companies may start looking more like software companies as their devices get more complex).

    I think you've also hit on a major issue going forward: Microsoft is going to have to focus on these not-PCs a lot more seriously in the future. Instead of trying to scale Windows down, it needs a MCE-esque approach to these "fast enough" devices. Apple made the right first step with the iPhone OS, Microsoft can't stand by idle for too long without a good alternative. And MS does love x86... :)

    Take care,
    Anand
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