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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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.