HP Z800Hyper threading
My Z800 runs 2 X5690s. Both processors are visible in OpenHardwareMonitor and CPUID. However if I turn hyper threading on in the BIOS, I can see CPU 0, but not CPU 1. It exists in the BIOS, but is not visible through the software I mentioned. Does the CPU get bypassed? Do I only get the performance of one CPU?
i'm going to guess that the OS (not mentioned..?) was installed with only one cpu installed, and the sec one was installed at a later date this can cause the OS to not correctly report the current cpu configuration some os's below win 7 do not correctly support multiple cpu's or multi core single cpu's
are your cpu's the same stepping? and production units? engineering samples/non production cpu's can have parts of the cpu that are not working such as the QPI links
are you running the latest bios? has it been set to factory defaults