In Windows NT 4.0, multi-processor support required that the Stepping levels on your processors be matched.

Windows 2000 will run with mismatched Stepping levels, though you may experience erratic behavior.

If Windows 2000 detects mismatched CPU Stepping, you receive a System Event log entry similar to:

   -------------------------------------------------------------------------
   Event ID Count Component    Message sample                              
   -------------------------------------------------------------------------

   I   41    32   Application  The CPUs in this multiprocessor system are  
                  Popup        not all the same revision level.  To use all
                               processors the operating system restricts    
                               itself to the features of the least capable  
                               processor in the system.  Should problems    
                               occur with this system, contact the CPU      
                               manufacturer to see if this mix of processors
                               is supported.