The above forms of the MOV instruction store or load the DR0, DR1, DR2, DR3, DR6 and DR7 debug resisters to or from a general purpose register.
Thirty-two bit operands are always used with these instructions, regardless of the operand-size attribute.
When the DE (Debug Extension) bit in CR4 is clear, MOV instructions using debug registers operate in a manner that is compatible with Intel386 and Intel486 CPUs. References to DR4 and DR5 refer to DR6 and DR7, respectively. When the DE bit in CR4 is set, attempts to run MOV instructions using DR4 and DR5 result in an Undefined Opcode (#UD) exception.