L3 is a substitute for the size you cant make the L2. Just as the L2 is the same for the L1. Or main memory is for L2/L3 etc.
In the Gallatin it was used to give a small boost, but at a big price. AMD is abit different since its stuck to the way they made their quadcore design and "lacked" cache knowhow if you can say that.
So a L3 only makes sense if you cant make the same size in a L2. It could be 8MB L2 is too much for Intel, but looking on the 6MB on penryn...
Another example is current Core 2 Xeon offerings, including MP have been completely ridden of L3.
I think many want Nehalem to be a K10 copy in design.
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