We knew that Intel's Sandy Bridge-E chips were big and complicated to make, but what we didn't expect was that Intel was going to continuously keep running into problems. The current C1 stepping is apparently having problems with VT-d, not a major issue for most consumers' maybe, but it's a huge problem when it comes to Xeon chips and as such Intel is working on the C2 stepping to fix this "errata".

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Sandy Bridge-E should hit C2 stepping after launch