I have Dell Precision T5400 workstation with two Intel Xeon processors. One a x5450 (quad core) and a e5450 (quad core). Both CPUs are recognised in the BIOS
I can not even install Windows with 2 processors installed. First I have to pull out one of them, then install windows. If I put the second processor back in I get error 'Multi processor not supported'.
I can work around that by booting with a single CPU and in System configuration -> Boot advanced options select the checkbox 'Number of processors' and set it to four (4 because that is about processor cores).
After that I can start windows and it wil use a single CPU.
Note that Device manager see 8 cores (2 CPUs).
Task manager see just 4 cores (in performance tab).
I installed Windows 10 Pro (updated from 8.1 Pro), and OS see just one processor.
Does anyone knows what is the problem?