This instruction is provided for compatibility with the Intel 286 processor; programs for the Pentium processor should use the MOV ..., CR0 instruction.

When the destination is a 32-bit register, the 16-bit source operand is copied into the lower 16 bits of the destination register, and the upper 16 bits of the register are undefined. With a 16-bit register operand, only the lower 16 bits of the destination are affected (the upper 16 bits remain unchanged). With a memory operand, the source is written to memory as a 16-bit quantity, regardless of operand size. As a result, 32-bit software should always treat the destination as 16-bits and mask bits 16-31, if necessary.