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Closer Look at Clarkdale Processor

Trying to expand the application field for LGA1156 platform, which so far has only had pretty expensive quad-core solutions in its arsenal, Intel intended Clarkdale to become an inexpensive dual-core solution. However, since it features an integrated graphics core, it becomes almost as complex internally as quad-core Lynnfield processors. And it means that despite the use of new 32 nm manufacturing process, Clarkdale processors production costs can easily become so high that it would make absolutely no sense for the manufacturer to promote these solutions in the low-end market segment.

Therefore, trying to lower the production costs of the new CPU, Intel suggested a unique design based not on a single monolithic semiconductor die of a comparatively large size, but on two relatively small dies put into a single CPU packaging. These two dies have separate functionality. The first die of about 78 mm2 is the actual dual-core processor, while the second 38 mm2 larger die is the GPU. However, even with this pretty natural distribution of responsibilities Clarkdale offers quite a few very interesting design concepts. The thing is that this implementation of the processor die features only two computational cores and an L3 cache. All North Bridge components, including the memory controller and PCI Express bus controller found their place in the GPU die.

We ended up with a very interesting picture: although Intel claims that they have combined the processor with the chipset North Bridge, if we dig a little deeper LGA1156 systems with Clarkdale processors look structurally the same as the previous generation platforms. The North Bridge is still there, it even exists as an individual semiconductor die. The only difference is that now this die doesn’t have its own packaging and is hidden inside the CPU case. Nevertheless, the FSB bus has really sunk into oblivion. Instead there is high-speed QPI interface used to connect the processor die and the North Bridge die within single packaging.

In fact, the processor die is manufactured using new 32 nm process. There are no special innovations in this manufacturing process: it produces transistors using high-k dielectric and metal gates like the ones in Intel’s 45 nm semiconductor dies. However, even by simply making these transistors smaller, Intel could speed up their switching, lower their heat dissipation and reduce the overall die size, which totally justifies the introduction of the new manufacturing process and use of immersion lithography equipment in Intel’s fabs. Clarkdale features a die of the same size as Wolfdale-3M used in Core 2 Duo E7000 CPUs, but the 32 nm processor has more cache memory. However, it wouldn’t be totally correct to call Clarkdale a fully 32 nm CPU. The thing is that the second semiconductor die containing the GPU and North Bridge is manufactured with 45 nm technological process.

The processor die contains two cores with Nehalem microarchitecture supporting Hyper-Threading technology. Therefore, although Clarkdale is a dual-core CPU, the operating system sees it as having four cores. And this particular fact allows Intel to position top Clarkdale models also as alternatives to quad-core LGA775 processors. L3 cache memory, which is also located inside the 32 nm processor die, is 4 MB big. So, compared with Lynnfield, Clarkdale has not only half the cores, but also half the L3 cache memory.


32 nm Clarkdale processor core

Most of the die is occupied by the graphics core, which represents the next generation of the Intel GMA. Compared with GMA X4500 built into Intel G45 LGA775 chipsets, the new graphics core has 12 shader processors instead of 10, works at slightly higher frequency and can use more memory for its needs. Nevertheless, its general performance level is still that of an integrated solution, so Clarkdale has no intention to become an alternative to discrete graphics cards.


Click to enlarge

The second die holds not only the graphics core but also a dual-channel memory controller supporting DDR3 SDRAM. I have to say that unlike the memory controller in Lynnfield processors, the one in Clarkdale supports only DDR3-1067 and DDR3-1333 memory, but in nominal mode when the CPU is not overclocked it can’t work with DDR3-1600. Moreover, the actual performance of the memory subsystem on Clarkdale based platforms will also be a little lower because the memory controller and the processor are located in two physically different semiconductor dies connected via the internal QPI bus.

Another important functional knot located in the North Bridge semiconductor die is the graphics bus controller. It uses PCI Express 2.0 protocol and supports 16 lanes that can be combined into a single PCI Express x16 bus or split into two PCI Express x8 busses. However, this split is only possible when the CPU is installed in an Intel P55 based mainboard.

 
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