Stores the contents of the global descriptor table register (GDTR) or the interrupt descriptor table register (IDTR) in the destination operand. The destination operand specifies a 6-byte memory location. If the operand-size attribute is 32 bits, the 16-bit limit field of the register is stored in the lower 2 bytes of the memory location and the 32-bit base address is stored in the upper 4 bytes. If the operand-size attribute is 16 bits, the limit is stored in the lower 2 bytes and the 24-bit base address is stored in the third, fourth, and fifth byte, with the sixth byte filled with 0s.
The SGDT and SIDT instructions are only useful in operating-system software; however, they can be used in application programs without causing an exception to be generated.
See "LGDT/LIDT - Load Global/Interrupt Descriptor Table Register" in this chapter for information on loading the GDTR and IDTR.