Monday, October 25, 2010

Intel's 45 nanometer Q9505S

In the Intel lineup, the Q9505S is a freak.  If I were to tell you that the performance of Intel's flagship 45nm quad-core processor (QX9650) would be delivered 2-years later at one third the cost and one half the power consumption you might conclude that Moore's Law had cycled again and the new processor benefited from a 32nm die shrink.  This is what makes the Q9505S such a strange creature - these benefits were surprisingly reaped all within the same 45nm tech node.  What gives?

For starters, it was released quite recently, two years after the first 45nm Core 2 quad-core processor, the QX9650, and consumes half the power at 65-watt TDP vs 130-watt TDP, and achieves approximately the same clock speed at 2.83ghz vs 3ghz.  Because the processor architecture is the same (Core 2 quad), there are only a few possible sources for the power efficiency gains.

One possibility is an improved layout, i.e. placement-and-routing of the transistors and wires that implement the Core 2 architecture.  It makes sense that only slight improvements would have been made here because Intel spends many man-hours hand-crafting the circuitry in the first place, and the Q9505S is seemingly not a high volume product that would merit follow-on hand-crafting.  Another source of efficiency gains is obtaining a sweet spot of 6MB for the L2 cache, which is 50% less than the 130 watt 12MB Core-2-quads, and 50% more than the 4MB Core-2-quads.

Perhaps most interesting is the implication that Q9505S is a beneficiary of improved fabrication technology within the 45nm tech node, long after the original 45nm debut.  Additional evidence for this is that mobile quad-core 2.53ghz parts (e.g. QX9300) with similar power efficiency to the Q9505S (45 watt TDP) were available a full year prior to the Q9505S, but cost much more (~$1k), indicating that the yield of processors with those specs was quite low.  Given the additional year for developing the 45nm process, the yield for such processor specs must have improved by a large margin to allow their release at much lower prices - these types of improvements usually come from Moore's Law die shrinks but in this case it was all within the 45nm process.

45nm also stands out as an unusual tech node, having been credited as the greatest advancement in semiconductors in 40 years by Gordon Moore himself.  This was due to overcoming difficulties in fabricating 45nm transistors by changing the elements used to makeup of the gate wires and insulation (so called "high-k metal gate").  This same technology is also being used in 32nm, begging the question as to whether 32nm will see similar delayed improvements.   This would be just what Intel needs in order to deliver 3ghz 8-core Sandy Bridge processors before Ivy bridge's 22nm fabrication technology is ready.

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