Intel's Atom Architecture: The Journey Begins
by Anand Lal Shimpi on April 2, 2008 12:05 AM EST- Posted in
- CPUs
Fighting Power Consumption...with a Longer Pipeline?
Atom's pipeline is a fairly deep 16 stages, with a 13 stage mispredict penalty. Note that this is longer than the Core 2 Duo's 14 stage pipeline, which is surprising given the low power focus the design team had for Atom.
A 16-stage pipeline complete with 3 instruction fetch and 3 instruction decode stages, more than expected
Longer pipelines are generally associated with greater power consumption especially as of late due to the Pentium 4's tenure. Intel gave us three reasons for the long pipeline:
1) Caches
2) Decoder
3) SMT
When faced with a decision between trading off latency for power, the Austin design team always favored keeping power low, even if it meant increasing latencies. Atom doesn't fire the large banks of its caches unless the cache controller knows there's a true hit in the cache, unfortunately this increases the access latency of the cache. In order to keep clock speeds high, these cache accesses have to be further pipelined. The benefit is that power is kept low; Atom keeps things as physically tagged caches to avoid the power burden of a virtually tagged cache.
The same sort of latency tradeoff is made in the decoding stages. Remember the slow vs. fast paths through the decoders? The slow path is higher latency but is guaranteed to properly decode an instruction, the added latency forces Atom to have three decoding stages instead of two.
Finally there are some algorithms in which SMT added a stage or two to the pipeline, the end result being a fairly lengthy pipeline for such a simple CPU. The reasoning however makes sense; there is no NetBurst nonsense here, all of these decisions were made to keep power consumption as low as possible while hitting the right frequency targets. As a fairly simple two-issue core, Atom needs clock speed in order to give us the sort of performance we are expecting of it.
Facebook
Twitter
RSS
46 Comments
View All Comments
FlakeCannon - Wednesday, April 2, 2008 - link
This was an absolutely fantastic article as far as I'm concerned. One of the best I've read from AnandTech. I'm truly impressed with the amount of effort and dedication that the engineers at Intel put into the Atom. Thought the consumer may not see its importance today the Atom will continue to develop one throughout the next 2 years and show why this is such a huge step in the right direction. I really think that this article outlines very well the architecture involved and where it intends to lead Intel and others in the future.I'm always impressed to see Intel take architecture that was revolutionary in its time 15 years ago in the Pentium and Pentium Pro and resurrect it in modern day fashion with help of the Dothan Pentium M architecture and even things borrowed from the miserable Netburst technology that 15 years later I believe will once again create a product revolutionary in nature. I was never able to appreciate it in the days of the Pentium but certainly can now.
This is one product I think is deserving of being excited about.
fitten - Wednesday, April 2, 2008 - link
What does an on-die memory controller have to do with ILP?Anand Lal Shimpi - Wednesday, April 2, 2008 - link
Woops, I've clarified the statement :)Take care,
Anand
erwos - Wednesday, April 2, 2008 - link
I was thinking that this would be a fantastic platform for making a small, silent HTPC box for doing streaming media, but the lack of 1080p output kills that to a large extent. I know it's not a big priority for the first revision given the UMPC targeting, but I hope the "Atom 2" does try to squeeze that feature in.FITCamaro - Wednesday, April 2, 2008 - link
It could always be paired with a different, more capable graphics core.ltcommanderdata - Wednesday, April 2, 2008 - link
It;d be very interesting to see how the 1.86GHz Silverthorne stacks up against a 1.8GHz P4 Northwood, a 1.86GHz Dothan, a 1.8GHz Conroe-L based Celeron, and a 1.8GHz Athlon 64.I wonder if Apple is going to refresh AppleTV with Silverthorne since it seems ideal with replace the current 1GHz ULV Dothan in there.
yyrkoon - Wednesday, April 2, 2008 - link
Well at least Intel did not name their Atom CPUs the 'Atom Z80' . . . heh.Anyways, this is good for our future, as the mITX, and pITX 'systems' now days are still kind of large-ish, and cost quite a bit of money for what they are. Though, I think that putting a web browser on just any old appliance in the house would be way overkill, and possibly a very serious mistake. A TV with a web browser ? An Oven ? Please . . . this is why we have PCs, and micro mobile devices.
Recently a friend and myself have been working on an embedded project, and I can see the potential here, but a 'problem' does exist. Some of the things you would want to do with such a processor . . . well lets just say there still would not be enough processing power. That being said, I do not see why these could not help make a TVs/HD-DVD player menu operate faster.
pugster - Thursday, April 3, 2008 - link
It certainly sounds nice, but the atom processor cost alot because some of the higher end models cost more than $100 each. I find it surprising that their Polosbo chipset is manufactured at 130mm. It probably came from one of their foundries that was due to upgrade to 32mm sometime next year anyways. They could've earily manufactured at 65mm.Somehow I don't see their product as mature and maybe the next gen product they would have a cpu and the north/south bridge in the same die.
lopri - Wednesday, April 2, 2008 - link
I honestly don't get the excitement. Should I? I mean, I wouldn't feel comfortable with one gigantic company controlling every single electronics in our life. If Intel opens up the X86 and everyone can compete on even end, then maybe. Since that won't happen, the future looks scary enough.clnee55 - Wednesday, April 2, 2008 - link
NO, how can you get excitement. I am already bored with your conspiracy theory. Let's talk about tecnical issue here.