Intel IA-32 - Manual (Page 236)

5-60 Vol. 3A
INTERRUPT AND EXCEPTION HANDLING
Program State Change
The machine-check mechanism is enabled by setting the MCE flag in control register CR4.
For the Pentium 4, Intel Xeon, P6 family, and Pentium processors, a program-state change
always accompanies a machine-check exception, and an abort class exception is generated. For
abort exceptions, information about the exception can be collected from the machine-check
MSRs, but the program cannot generally be restarted.
If the machine-check mechanism is not enabled (the MCE flag in control register CR4 is clear),
a machine-check exception causes the processor to enter the shutdown state.