The 16-bit forms of the SGDT and SIDT instruction are compatible with the Intel 286 processor, if the value in the upper eight bits is not referenced. The Intel 286 processor stores 1's in these upper bits, whereas the 32-bit processors store 0's if the operand-size attribute is 16 bits. These bits were specified as undefined by the SGDT and SIDT instructions in the 80286 Programming Reference Manual (Intel Order No. 210498).