Intel Sandy Bridge-E Review - Core i7-3960X and X79 Chipset Tested
Sandy Bridge-E is just what you expect
It has been more than three years since Intel released the first Core i7 processor built around the Nehalem CPU architecture along with the X58 chipset. It quickly became the platform of choice for the enthusiast market (gamers and overclockers), and remained in that role even as the world of processors evolved around it with the release of Westmere and Sandy Bridge. Yes, we have been big supporters of the Sandy Bridge Core i7 parts for some time as the "new" platform of choice for gamers, but part of us always fondly remembered the days of Nehalem and X58.
Well, Intel shared the sentimentl and this holiday they are officially unveiling the Sandy Bridge-E platform and the X79 chipset. The "E" stands for enthusiast in this case and you'll find that many of the same decisions and patterns apply from the Nehalem release to this one. Nehalem and X58 was really meant as a workstation design but the performance and features were so good that Intel wanted to offer it to the high-end consumer as well. Sandy Bridge-E is the same thing - this design is clearly built for the high-profit areas of computing including workstation and servers but those that want the best available technology will find it pretty damn attractive as well.
But what actually makes a Sandy Bridge-E processor (now going with the Core i7-3xxx model naming scheme) different from the Sandy Bridge CPUs we have come to love since it was released in January of this year?
The Sandy Bridge-E Architecture
The answer might surprise you, but truthfully not a whole lot has changed. In fact, from a purely architectural stand point (when looking at the x86 processor cores), Sandy Bridge-E looks essentially identical to the cores found in currently available Sandy Bridge CPUs. You will see the same benefits of the additional AVX instruction set in applications that take advantage of it, a shared L3 cache that exists between all of the cores for data coherency and the ring bus introduced with Sandy Bridge is still there to move data between the cores, cache and uncore sections of the die.
Turbo Boost technology makes a return here as well with the updated 2.0 version in full effect - there are more steppings in scalability on this part than on the Nehalem or Westmere CPUs.
With that said, there are some important changes to take note of, starting with the absence of any and all Sandy Bridge aspects related to graphics and multimedia processing. The Sandy Bridge-E Core i7-39xx and i7-38xx parts will not have processor graphics of any kind on them, and while this isn't a big deal for the targeted users of high-end hardware like this, there is one drawback. Along with the GPU portion, the QuickSync technology is also absent from the design as it was dependent on the Intel HD Graphics technology for some of its processing. If you were a fan, as we were, of the QuickSync media transcoding applications that worked impressively fast, then you should be prepared to live without it again if you buy a SNB-E processor. Still, with 6-cores and 12-threads of processing, the Core i7-3960X should be able to handle media transcoding fairly well as we demonstrate in our benchmark testing.
The Sandy Bridge-E Die
A significant portion of the processor die is relegated to communication with the 40 lanes of PCI Express supported by Sandy Bridge-E. This is a VAST improvement over the current Sandy Bridge parts that only support 16 lanes. While PCI Express 3.0 support is not yet official on the SNB-E CPUs, all of the motherboard vendors we have talked to are comfortable with saying the combination of the new CPUs and X79 motherboards will run that communication protocol properly when supported cards are released in 2012. For whatever reason, Intel has decided to not validate the PCIe 3.0 capability of the processor directly and instead claims that it "believes that some PCIe devices may be able to achieve the 8GT/s PCIe transfer rate on X79". So...uh, there.
As all of the motherboard designs have shown you over the last several months, Sandy Bridge-E also moves from a dual-channel memory controller to a much higher bandwidth quad-channel memory controller. Theoretical memory bandwidth moves up to 51.2 GB/s and while some very specific applications will see (and take advantage of) this change, most consumer applications and games won't come close to seeing a 2x increase in performance. Still, those that complained about moving from a three-channel memory controller on Nehalem to the dual-channel on Sandy Bridge will be pleased to see a move forward in this area.
This, of course, means a new collection of memory module kits from Corsair and the like are in order. To take full advantage of your processor's performance, you are going to need to populate all four of those memory channels. We have already seen a few sets from Corsair that target the SNB-E buyer. Another good side effect of four memory channels is that you will (by default) have more memory in your system overall. Even if you go down to 2GB modules for each channel we are talking about an 8GB configuration and more likely a 16GB total system memory option for users that go with still very cost efficient 4GB DIMMs.
One interesting thing to note from looking at the die shot above is that there are two cores disabled on SNB-E. Those cores will surely be enabled on upcoming Xeon processors but I am still confused as to why Intel chose to keep them disabled completely. I understand that with 8 cores they weren't likely to be able to run at higher clock speeds than current Sandy Bridge processors, but offering a SKU that was 8-cores/16-threads deep at lower clock speeds could have been for consumers that really use heavily-threaded applications. As it stands now, Intel only has plans for 6-core and 4-core SNB-E processors.
Shared L3 cache size has also been increased up to a staggering 15MB on the Core i7-3960X flagship and 12MB on the Core i7-3930K. To put that in perspective, the current Core i7-2600K Sandy Bride processor and Core i7 Nehalem parts sport 8MB of L3 cache. From the die image we can gather that the Core i7-3960X is actually using all of the available cache size and any upcoming Xeons with 8-cores will have the same amount.
The new Sandy Bridge-E processors are larger than previous Nehalem or Sandy Bridge CPUs as inferred from the requirement of the new LGA2011 socket. The CPU die itself is built on the same 32nm process technology as the current generation Sandy Bridge and consists of 2.27 billion transistors in the form of a nearly square 434.72 mm2 die.