performance - Does the Intel i7 offer real improvement over its predecessors?

As the questions title asks, do the new processors from Intel offer real, as in noticeable, improvement over the previous quad core ones? What does the i7 actually offer that is new or is it simply a marketing gimmick?

Answer

Definitely does. You want to talk about Nehalem first, the quad-core should be discussed after that.

A very quick summary from the ArsTechnica article.
Nehalem-derived processors — if it's still appropriate to call them "processors" and not "systems-on-a-chip" (SoCs) — will mix the following elements in different proportions, depending on the platform and product:

• Number of cores


• Number of memory channels on the integrated memory controller


• Type of memory supported (registered and unregistered DDR3 or FB-DIMM)


• Number of links in the QuickPath interface (for scaling QuickPath bandwidth)


• L3 cache size


• Power management features


• Integrated graphics [we are talking on-chip here]

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References.