The Sandy Bridge Preview
by Anand Lal Shimpi on August 27, 2010 2:38 PM ESTA New Architecture
This is a first. Usually when we go into these performance previews we’re aware of the architecture we’re reviewing, all we’re missing are the intimate details of how well it performs. This was the case for Conroe, Nehalem and Lynnfield (we sat Westmere out until final hardware was ready). Sandy Bridge, is a different story entirely.
Here’s what we do know.
Sandy Bridge is a 32nm CPU with an on-die GPU. While Clarkdale/Arrandale have a 45nm GPU on package, Sandy Bridge moves the GPU transistors on die. Not only is the GPU on die but it shares the L3 cache of the CPU.
There are two different GPU configurations, referred to internally as 1 core or 2 cores. A single GPU core in this case refers to 6 EUs, Intel’s graphics processor equivalent (NVIDIA would call them CUDA cores). Sandy Bridge will be offered in configurations with 6 or 12 EUs.
While the numbers may not sound like much, the Sandy Bridge GPU is significantly redesigned compared to what’s out currently. Intel already announced a ~2x performance improvement compared to Clarkdale/Arrandale, and I can say that after testing Sandy Bridge Intel has been able to achieve at least that.
Both the CPU and GPU on SB will be able to turbo independently of one another. If you’re playing a game that uses more GPU than CPU, the CPU may run at stock speed (or lower) and the GPU can use the additional thermal headroom to clock up. The same applies in reverse if you’re running something computationally intensive.
On the CPU side little is known about the execution pipeline. Sandy Bridge enables support for AVX instructions, just like Bulldozer. The CPU will also have dedicated hardware video transcoding hardware to fend off advances by GPUs in the transcoding space.
Caches remain mostly unchanged. The L1 cache is still 64KB (32KB instruction + 32KB data) and the L2 is still a low latency 256KB. I measured both as still 4 and 10 cycles respectively. The L3 cache has changed however.
Only the Core i7 2600 has an 8MB L3 cache, the 2400, 2500 and 2600 have a 6MB L3 and the 2100 has a 3MB L3. The L3 size should matter more with Sandy Bridge due to the fact that it’s shared by the GPU in those cases where the integrated graphics is active. I am a bit puzzled why Intel strayed from the steadfast 2MB L3 per core Nehalem’s lead architect wanted to commit to. I guess I’ll find out more from him at IDF :)
The other change appears to either be L3 cache latency or prefetcher aggressiveness, or both. Although most third party tools don’t accurately measure L3 latency they can usually give you a rough idea of latency changes between similar architectures. In this case I turned to cachemem which reported Sandy Bridge’s L3 latency as 26 cycles, down from ~35 in Lynnfield (Lynnfield’s actual L3 latency is 42 clocks).
As I mentioned before, I’m not sure whether this is the result of a lower latency L3 cache or more aggressive prefetchers, or both. I had limited time with the system and was unfortunately unable to do much more.
And that’s about it. I can fit everything I know about Sandy Bridge onto a single page and even then it’s not telling us much. We’ll certainly find out more at IDF next month. What I will say is this: Sandy Bridge is not a minor update. As you’ll soon see, the performance improvements the CPU will offer across the board will make most anyone want to upgrade.
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Touche - Friday, August 27, 2010 - link
And the naming...OMG!There will be i7 processors that require three (3 !!!) different sockets! Maybe even 4 when 2011 comes. Intel can't get their naming right for quite some time now, but they've outdone themselves this time.
ereavis - Monday, August 30, 2010 - link
Processor names really should mean something, even if AMD and Intel don't agree. It's annoying that I have to wikipedia a processor (or memorize a thousand processors) to know what it is. We are still getting quotes for three year old Opterons and Xeons (that we're using as desktops no less), those only add to the annoyance.What ends up happening - good for Intel bad for technology advancement - is non IT type people buying computers are buying DDR2-667 based three-year old desktop processors.
BSMonitor - Friday, August 27, 2010 - link
Ummm, but Bulldozer comes with AM3-r2... Just a sketchier way of saying new MB needed.At least this new Intel isn't trying to BS you. Significant revisions to the architecture require different pin layouts/counts... It is inevitable with processor evolution.
Touche - Friday, August 27, 2010 - link
Actually, it should be AM3 compatible:http://www.tomshardware.com/reviews/bulldozer-bobc...
Even if it's not, AM2/AM3 lasted quite some time.
"At least this new Intel isn't trying to BS you. Significant revisions to the architecture require different pin layouts/counts... It is inevitable with processor evolution."
They know in advance what they need and could design a socket to support multiple processors. And i7/i5/i3 definitely don't need different ones.
BSMonitor - Friday, August 27, 2010 - link
"Even if it's not, AM2/AM3 lasted quite some time."Not all AM2 processors were compatible with AM2+ MB or vice versa, not all AM3 processors compatible on AM2+ MB.
It's still 3 different sockets.
Marketing buddy, marketing.
By the time 1366 is replaced, it will have been on the market for 4 years.
stmok - Saturday, August 28, 2010 - link
Eh, no its not. Bulldozer does NOT work with non-AM3+ mobosAMD engineers made a decision not to make it backward compatible for three reasons.
(1) No one but enthusiasts upgrade their CPUs. People in the real world upgrade their whole computer.
(2) Bulldozer introduces new features that won't work with existing Socket AM3 mobos. (Isn't it bloody obvious when they have to introduce a new socket specification?)
(3) It would cost more money and delays if they were to make a backward compatible version of Bulldozer.
As a result, they made a compromise:
You can take your existing AM3 CPU to AM3+ mobos, while you wait for Bulldozer to arrive. BUT, you can NOT upgrade your existing AM3 based system to Bulldozer.
Simply put...
AM3+ CPU and AM3+ mobo = OK
AM3 CPU and AM3+ mobo = OK
AM3+ CPU and AM3 mobo = Sorry. No.
So it doesn't matter if AMD "Bulldozer" or Intel "Sandy Bridge". You will need a new mobo.
Ard - Friday, August 27, 2010 - link
AMD seriously has their work cut out for them with Bulldozer. The lowest end Sandy Bridge processor absolutely trounced the competition. It's insane what Intel is pulling off here, especially in the integrated graphics arena. Really makes me hope Larrabee comes back as a discrete product in the next few years.dgz - Saturday, August 28, 2010 - link
poor kid, you don't realize 2400 is not nearly lowest end.Finally - Sunday, August 29, 2010 - link
Doesn't that make him a "(filthy) rich kid"?Quodlibet - Friday, August 27, 2010 - link
- based on the shown roadmap, the replacement for the i5 760 is actually the i5 2500(K).- i7 will have even better performance with 8 MB L3 Cache and higher graphics turbo. So there is even more performance potential in the SandyBridge die that Intel could unlock for lower SKUs if needed.