If a prospective buyer wants to know what features his CPU of choice actually supports, he can determine this by looking at the last 5 numbers of the product code, which can be found on every CPU box. For example, the identifier SL836 indicates a 90nm part with HT technology, 04B platform compatibility, and 64-bit support.
You can find the product code here.
This denotes the compatibility with the 04A or 04B platform (these have different power requirements).
The SL-SPEC number on the CPU's heat spreader is also visible through the box's little plastic widow.
Despite its larger 2 MB L2 cache, the 600 series doesn't feature much of a gain in performance. The problem here lies with the larger cache's higher latencies. As a result, the average performance boost of the 600 series CPUs over the equivalent model of the 500 series roughly corresponds to about a 200 MHz clock speed difference. Mainly, this applies to applications that actually benefit from a larger cache, such as games.
For a long time after the introduction of the Pentium 4 660, things were very quiet. A full seven months passed before Intel followed up with the 3.8 GHz Pentium 4 670 in September 2005.
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