The SGDT and SIDT instructions copy the contents of the descriptor table register to the six bytes of memory indicated by the operand. The LIMIT field of the register is assigned to the first word at the effective address. If the operand-size attribute is 16 bits, the next three bytes are assigned the BASE field of the register, and the fourth byte is undefined. Otherwise, if the operand-size attribute is 32 bits, the next four bytes are assigned the 32-bit BASE field of the register.
The SGDT and SIDT instructions are used only in operating system software; they are not used in application programs.