Barcelona Architecture: AMD on the Counterattack
by Anand Lal Shimpi on March 1, 2007 12:05 AM EST- Posted in
- CPUs
The Chip
Barcelona is AMD's first quad-core processor, featuring four cores on a single 65nm die. Unlike Intel's quad-core Kentsfield, Barcelona is not made up of two dual core die, which is why AMD calls it a "native" quad core solution. Although there is a technical performance advantage to AMD's approach, we're unsure if it's something that will be visible in real world testing.
Built on AMD's 65nm process, Barcelona is a more complex design than the K8 requiring a total of 11 metal layers compared to 9 for K8 and 8 for Core 2. AMD has required more metal layers at the same process generation than Intel in previous years, so Barcelona is not unique. Additional metal layers make manufacturing a bit more complicated, but there are no significant downsides to the end user.
With four cores and an optional 2MB of L3 cache on-die, Barcelona weighs in at 463 million transistors. At 463 million transistors, Barcelona is 119 million transistors shy of Kentsfield's 582M count. The lower transistor count boils down to a lack of cache; each Barcelona core has a 128KB L1 cache and a 512KB L2 cache, with all four cores sharing a 2MB L3 cache, for a total of 4.5MB of cache on-die. Each of the two die that compose a single Kentsfield have two cores, each core with its own 64KB L1 and a shared 4MB L2. A single Kentsfield chip has a total of 8.25MB of cache on-die, over 80% more than Barcelona, thus explaining the 25.6% increase in transistor count.
However, Barcelona is far more than a quad-core K8 with an L3 cache. We estimate the number of non-cache transistors in a dual-core Athlon 64 X2 to be approximately 94M, and the Barcelona core is around 247M; even doubling the dual-core K8 figure won't get you close to Barcelona. Note that simply doubling the 94M number also isn't an accurate comparison as Barcelona only features a single on-die Northbridge. In essence, there are more than 60M additional transistors (or more than 15M per core) that went into architectural enhancements outside of more cores and cache in Barcelona.
Barcelona is AMD's first quad-core processor, featuring four cores on a single 65nm die. Unlike Intel's quad-core Kentsfield, Barcelona is not made up of two dual core die, which is why AMD calls it a "native" quad core solution. Although there is a technical performance advantage to AMD's approach, we're unsure if it's something that will be visible in real world testing.
Built on AMD's 65nm process, Barcelona is a more complex design than the K8 requiring a total of 11 metal layers compared to 9 for K8 and 8 for Core 2. AMD has required more metal layers at the same process generation than Intel in previous years, so Barcelona is not unique. Additional metal layers make manufacturing a bit more complicated, but there are no significant downsides to the end user.
With four cores and an optional 2MB of L3 cache on-die, Barcelona weighs in at 463 million transistors. At 463 million transistors, Barcelona is 119 million transistors shy of Kentsfield's 582M count. The lower transistor count boils down to a lack of cache; each Barcelona core has a 128KB L1 cache and a 512KB L2 cache, with all four cores sharing a 2MB L3 cache, for a total of 4.5MB of cache on-die. Each of the two die that compose a single Kentsfield have two cores, each core with its own 64KB L1 and a shared 4MB L2. A single Kentsfield chip has a total of 8.25MB of cache on-die, over 80% more than Barcelona, thus explaining the 25.6% increase in transistor count.
However, Barcelona is far more than a quad-core K8 with an L3 cache. We estimate the number of non-cache transistors in a dual-core Athlon 64 X2 to be approximately 94M, and the Barcelona core is around 247M; even doubling the dual-core K8 figure won't get you close to Barcelona. Note that simply doubling the 94M number also isn't an accurate comparison as Barcelona only features a single on-die Northbridge. In essence, there are more than 60M additional transistors (or more than 15M per core) that went into architectural enhancements outside of more cores and cache in Barcelona.
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JustKidding - Friday, March 2, 2007 - link
So what you are saying is that it's not the size of your cache that matters as much as how well you use it.VooDooAddict - Thursday, March 1, 2007 - link
With Cache size differences usually having small impact on performance for Athlon64s, the slight trade off for better yields and margins seems the better choice for AMD here.
Regs - Thursday, March 1, 2007 - link
Where was this article 8 months ago? ;)I agree with Anands closing article that AMD now needs it's own "snowball effect" for the next couple of years. 4-5 years with a sitting target against a giant like Intel prooved to be costly in terms of competivness.
We all saw it coming when Intel developed the first Pentium M. It looks like AMD got the message as well and started the Barcelona project. Maybe AMD learned their lesson.
iwodo - Thursday, March 1, 2007 - link
So bascially all intel 's C2D improvement are made into Barcelona. And apart from Virtualization improvement there are nothing new from AMD that Intel doesn't have?On performance note Barcelona doesn't seem to offer better clock scaling. I.e even if it is 30% faster then its current K8 it will only have slight advantage against C2D clock per clock. Not to mention it is up against Penryn. Although Penryn is nothing much then a few minor tweaks and more cache. It does allow intel to scale higher in clock speed.
And given AMD slow roll out rate, and AMD limited production capacity Barcelona never seem like much of a threat.
The article does not mention anything about FP improvement. Are AMD keeping them secret for now or is that all we are going to see?
Spoelie - Thursday, March 1, 2007 - link
The FP improvement is the SSE improvement, and according to the theory it's more powerful than what core2 duo is offering.There are improvements mentioned that are not in core2 (+ other way around, like instruction fusing), and improvements that are inspired on the same principle but implemented differently. The architectures themselves differ widely (see earlier article that compares K8 with Core2 - reservation station etc.) so different implementations of principally the same optimizations on a different architecture will have vastly different effects. Even after these improvements, the capabilities (how much can you decode, etc) of each read nothing alike. And if it were all the same, AMD has the platform advantage, so it would still end up faster by virtue of nothing else but that. Some guesstimates made by varying sites would put Barcelona ahead in FP code and at the same level or slightly behind in INT code. But those are just guesstimates.
What I'm trying to say here is that barcelona is still very different from core2, and that we just don't know yet in which direction the pendulum will swing ;)
Shintai - Thursday, March 1, 2007 - link
No....precisely in theory is where Barcelona lacks. Core 2 Duo could in theory do 6 64bit or 3 128bit SSE instructions per cycle. Barcelona can do 4 64bit or 2 128bit. AMD provided this information aswell.Griswold - Thursday, March 1, 2007 - link
Wishful thinking.Spoelie - Thursday, March 1, 2007 - link
Hmmm, in the earlier article, there was explicit emphasis on the fact that 2 of the 3 units are symmetric in core2, but I'm not too sure what it means. It does imply however that those 3 units of core2 can only be used fully in certain combinations, and are not 3 independent units. On 128-bit performance, what was said is this: "so the Core architecture has essentially at least 2 times the processing power here [compared to K8]". Not 3 times, but "at least" 2 times, so again the 3 times will probably only be in certain situations.The next paragraph said this:
"With 64-bit FP, Core can do 4 Double Precision FP calculations per cycle, while the *Athlon64* can do 3."
So K8 was not at such a big disadvantage when it came to 64-bit SSE, if Barcelona doubles everything SSE, it should come ahead in this area.
So to me it looks like for 128-bit, core2 will be faster in some situations, on par in others, and for 64-bit, Barcelona would be ahead.
If this is wrong, I do not know where some of the articles I read over time came from, implying Barcelona would be better overall in SSE.
Shintai - Friday, March 2, 2007 - link
Core 2 got 3 individual SSE ports:http://www.realworldtech.com/page.cfm?ArticleID=RW...">http://www.realworldtech.com/page.cfm?ArticleID=RW...
AMD says 4 double:
http://www.anandtech.com/showdoc.aspx?i=2768&p...">http://www.anandtech.com/showdoc.aspx?i=2768&p...
And 64 or 128bit doesnt matter. I dont know how you think that way.
Barcelona got 2 SSE ports. They are able to do 2 128bit or 4 64bit. Most 128bit actually contains 2 64bit or 4 32bit.
Core 2 got 3 SSE ports. They are able to do 3 128bit or 6 64bit.
flyck - Friday, March 2, 2007 - link
core duo has 3 SSE units but they are not symmetric, meaning that not every unit can execute all commands. Core duo can do at best 4DP flops/ cycle. the same as barcelona.