80386 Programmer's Reference Manual -- Opcode SMSW

SMSW -- Store Machine Status Word

OpcodeInstructionClocks DescriptionExample
0F 01 /4smsww r/m162/3,pm=2/2 Store machine status word to EA wordsmsww %cx
smsww (%ebx,1)
smsww (%ebx,2)
smsww (%ebx,%ebp,1)


r/m16 := MSW;


SMSW stores the machine status word (part of CR0) in the two-byte register or memory location indicated by the effective address operand.

Flags Affected


Protected Mode Exceptions

#GP(0) if the result is in a nonwritable segment; #GP(0) for an illegal memory operand effective address in the CS, DS, ES, FS, or GS segments; #SS(0) for an illegal address in the SS segment; #PF(fault-code) for a page fault

Real Address Mode Exceptions

Interrupt 13 if any part of the operand would lie outside of the effective address space from 0 to 0FFFFH

Virtual 8086 Mode Exceptions

Same exceptions as in Real Address Mode; #PF(fault-code) for a page fault


This instruction is provided for compatibility with the 80286; 80386 programs should use MOV ..., CR0.

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