This also reminds me that NT4 before SP6 had a check that CPUID leaf 0 returned a maximum CPUID value less than 4, and leaf 3 was taken for the PSN. When Presco

This also reminds me that NT4 before SP6 had a check that CPUID leaf 0 returned a maximum CPUID value less than 4, and leaf 3 was taken for the PSN. When Prescott arrived, Intel had to add a MSR to limit the returned value.