Hi @old_geekster,
Many thanks for your attention.
This Z640 is configured with 1x Xeon E5-2683v3 and Windows 7 Pro 64-bit. I’ve used 1x, 2x and 4x DIMMs of 32GB to check it. The fans always rotated at high speed 2000RPM and made great noise. I did some pictures with “HP Performance Advisor” to describe this problem.
1.) 1x 32GB 4DRx4 PC4-2133P-L Samsung
2.) 2x 32GB 4DRx4 PC4-2133P-L Samsung
When I used 8GB or 16GB DDR4 memory: 4x 8GB 1Rx4 PC4-2400T-R or 4x 16GB 2Rx4 PC4-2133P-R. All fans rotated at 500~600RPM. The Z640 is very quiet.
All tests are done using same FAN Idle mode: -------
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