NASM 2.05 based x86 Instruction Reference[ch355]

A.5.329 WRMSR: Write Model-Specific Registers WRMSR ; 0F 30 [PENT] WRMSR writes the value in EDX:EAX to the processor Model-Specific Register (MSR) whose index is stored in ECX. See also RDMSR (section A.5.270).