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What's the difference of QDF and S-spec code ?


1. QDF code is for QS sample, right ?

2. what's the sample called after QS, I mean mass production CPUs.

3. what's S-spec code for ?

4. how to define the stepping of processors ? A0-A1-B0-B1... ?

5. The product marked S-spec code is newer than products which marked QDF code? and the stepping is also newer?

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Super User

To the best of my knowledge,

  1. QDF Number is a four digit code used to distinguish between engineering samples.
  2. Once a processor is in pre-production, its S-Spec Number is used to represent it.
  3. S-Spec Numbers are a five-digit code used to identify products. Products are differentiated by their unique characteristics, for example, core speed, L2 cache size, package type, etc.
  4. Not sure that you are asking here. When errors are found in a processor, they may be fixable in microcode or they may require a silicon change - what Intel refers to as a 'metal layer change'. When metal layer changes are released, Intel changes the Stepping Code. A major set of metal layer changes or 'an improvement in the manufacturing process' will increment the Stepping Code's letter (i.e., An to Bn) while a minor set of metal layer changes will just increment the Stepping Code's number (i.e., B0 to B1).
  5. Yes, pre-production and production processors with S-Spec Numbers are definitely newer that engineering samples with QDF Numbers. I believe that the transition from engineering sample to pre-production sample is typically accompanied by a change in stepping. I do not believe that the transition from pre-production sample to production necessarily requires a change in stepping, however. Intel Customer Support may need to step in and qualify these statements.

Hope this helps,



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