Never use an undefined value ECx before usng the RDMsR or wRMsR instrucion If ECX = 0 before the read or write machine-specific register instruction, the value returned. EDX: EAX, is the machine check exception address.( EDX:EAX is where all data reside when the value is the machine check written or read from the model-specific registers.) If ECX =1 ,the value is the machine check exception type, if ECX = 0EH. the test register 12(TR12) is accessed. Note that these are internal registers designed for in-house testing. The contents of these registers are proprietary to Intel and should not be used during normal programming.