Intel's Atom Architecture: The Journey Begins
by Anand Lal Shimpi on April 2, 2008 12:05 AM EST- Posted in
- CPUs
Intel's Atom: Changing Intel from the Inside
For years at Intel the rule of thumb for power vs. performance was this: a designer could add a feature to a microprocessor design if you get a 1% increase in performance for at most a 2% increase in power. Unfortunately, it's thinking like that which gave us the NetBurst architecture used in the Pentium 4 and its derivatives.
The Intel Atom was the first Intel CPU to redefine the rule of thumb and now the requirement is that a designer may add a feature if it yields a 1% increase in performance for at most a 1% increase in power consumption. It's a pretty revolutionary change and it's one that will be seen in other Intel architectures as well (Nehalem comes to mind), but Atom was the first.
While Atom started as a single-issue, in-order microprocessor the Austin team quickly widened it to be a dual-issue core. The in-order decision stuck however.
Modern day x86 processors can operate on instructions out of program order. It's like if you had to tie your shoe and turn on the TV, you may choose to tie your shoe first and then walk over to the remote control to turn on the TV. You'd complete the quicker task first before moving onto the one that took more time since you didn't have the remote on hand. Processors that are capable of OoOE (Out of Order Execution) work in the same way; when data isn't available in their caches instead of idly waiting on the data, they can execute other instructions that are ready while waiting for the required data to be fetched from memory.
The problem with these out of order processors is that all of this instruction reordering takes up additional die space and increases power consumption. Performances goes up as well but remember, Intel's goal here wasn't to be the fastest, but to be fast enough. Thus the Atom remained an in-order CPU, incapable of executing instructions out of program order and Intel's first in-order x86 core since the original Pentium processor.
The decision to go in-order eliminated the need for much complex, power hungry circuitry. While you get good performance from out-of-order execution, the corresponding increase in scheduling complexity was simply too great for Atom at 45nm. Keep in mind that just as out-of-order execution wasn't feasible on Intel CPUs until the Pentium Pro, there may come a time where transistor size is small enough that it makes sense to implement an OoOE engine on Atom. I don't expect that you'll see such a change in the next 5 years however.
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adntaylor - Tuesday, April 8, 2008 - link
On that chart with price / power, you need to be clearer...For price, you show the combined price for CPU + Chipset. For power, you say just the CPU... so 0.65W for the CPU... but you're conveniently ignoring the >2W figure for the chipset!!! This absolutely flatters Intel wherever possible.
AMD are just as misleading - they describe the Geode LX as "1W" which excludes the non-CPU core parts of the chip (which is an integrated CPU + GMCH)
Just please be honest - the figures are out there in the Intel datasheets... it takes 10 minutes to check.
Clauzii - Friday, April 4, 2008 - link
I still have a PowerVR 4MB addon card, runnung in tandem with a Rage128Pro. Quite a combination w. 15 FPS in Tombraider. Constant(!) 15FPS, that is..Amazing what they actually achieved back in 95!
Clauzii - Friday, April 4, 2008 - link
Ooops!Totally misplaced that. Sorry.
wimaxltepro - Friday, April 4, 2008 - link
The Atom represents a shift in processor architecture that is the most dramatic departure for Intel since introduction of x86 processors... the philosophy of how computing itself occurs from centralized processors to distributed processing based on an extension of the popular x86 instruction set.The Atom is not about the immediate prospects for the Atom or Nehalem products: we will likely see members of Intel's new product family be used in embedded applications in consumer products and in areas where specialized communications processors are more the rule. While not optimized for use in specific networking applications, the products capitalize on the wide range of support available in IT/Networking to develop common functions that leverage the low cost, low power/processing capability to be used as a common denominator for a wide range of applications.
Intel has been built on the 'Wintel' architecture: massively integrated chips needed to handle the massively integrated operating systems and applications of Windows (and Apple) environments. The Atom allows migration and broadening out from that architectural motif to a very highly distributed architecture. So, the increased parallelism found in the internal chip architecture is enabling of changes in external system architectures and device applications that go well beyond the typical domain of Intel.. and right into the domain of 'personal wireless broadband' and SDWN, Smart Distributed Wireless broadband Network.
The decisions about in-order vs. out of-order instruction streams, memory architecture, I/O architecture have been made in light of the broad vision for how computing, networking and, out of hand, how wireless enabled broadband networking including WiMAX will occur. This should be understood for what it represents as a shift in direction for Intel both in response to broad industry shifts and as a trend setting development.
jtleon - Friday, April 4, 2008 - link
Thanks to all the flash player ads, etc., a mobile web device will continuously avoid switching to low power states. Thus one could argue that advertising will be carbon footprint enemy of the internet's future. This is already becoming the case for desktop/laptop machines.Without such continuous (arguably wasted) consumption of CPU power, then Intel's engineered power management might have a significant impact on the value of the Atom.
Regards,
jtleon
0WaxMan0 - Friday, April 4, 2008 - link
I am definatly much impressed and enthused by intels work here, the future looks interesting esp for those of us who like low power cross compatible computing products.However I have to point out that a low power modern x86 cpu has allready been done infact 4 years ago with AMD's Geode. While technically much weaker than the Atom and with out any where near the scalability (single core design etc.) the Geode has been available in the same TDP ranges for a good long while. Take a look here http://www.amdboard.com/geode.html">http://www.amdboard.com/geode.html for some old stuff.
I do hope that the Intel name and hype makes more of an impact than AMD managed.
whycode - Thursday, April 3, 2008 - link
Does the TDP quoted include the chipset? Or is that CPU only?IntelUser2000 - Thursday, April 3, 2008 - link
Anand, the Pentium M does not feature Macro Ops Fusion. Its Core 2 Duo that started Macro Ops Fusion.Anand Lal Shimpi - Thursday, April 3, 2008 - link
You're correct, I was referencing micro-op fusion. I've made the appropriate correction :)Take care,
Anand
squito - Wednesday, April 2, 2008 - link
Am I the only one shocked to see that Poulsbo is a 130nm part...