RE: Help me dell precision t5500 workstation with X5660 Hex Core showing 4 cores instead of 6
Couple of things I can think of. Firstly, perhaps the X5660 is defective. Happens sometimes.
Second possibility is that Windows is configured to only use 4 cores. Go to Cortana's search bar and type in msconfig.exe and hit enter. Click on the Boot tab, then hit 'Advanced Options'. Look at the "Number of processors" field and see if it's set to four cores.