Intel's Atom Architecture: The Journey Begins
by Anand Lal Shimpi on April 2, 2008 12:05 AM EST- Posted in
- CPUs
Gridless Clock Distribution
As you push the frequency limits in large, high performance CPUs like the Core 2, you need to minimize overhead in each clock period so you can do the maximum amount of work. Timing is key.
All functional blocks within a microprocessor operate on the same clock signal. You can think of the clock signal like a metronome or a heart beat; work only happens at every tick of the metronome, every beat of the heart or whenever the clock is logically "1" or "high".
There's a single clock signal that's distributed across the chip, but the more complex the chip and the more times the clock changes per second, the tougher it becomes to just make sure the clock gets to all parts of the chip.
In order to reach the absolute maximum frequencies possible, making sure the clock signal arrives at all parts of the chip at the same time with very little variation becomes increasingly important.
The most effective method of distributing this single clock across the chip is by using a metal grid to distribute this critical signal across a large, complex die. The problem with this metal grid is that although it makes sure the clock gets to all parts of the chip with very little skew, it has a huge capacitance and consumes tremendous amounts of power. Large CPU cores can spend 30 - 35% of their power budget simply on clock distribution. This would obviously not work for Atom.
While the Atom processor needs to run at relatively high frequencies, we're not talking about pushing 4GHz here. Without strenuous frequency requirements, a simpler form of clock distribution is ok. Atom uses a binary tree for clock distribution; the clock signal is sent from the PLL to the point of divergence, then fanned out into multiple trees of inverters and finally distributed vertically from each point of divergence to each FUB.
The binary tree approach significantly reduces the amount of current consumed to the point that less than 10% of Atom's power budget is spent on distributing the clock.
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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.