GDT Tutorial: Difference between revisions

: a reference to a descriptor you can load into a segment register; the selector is an offset of a descriptor table entry. These entries are 8 bytes long. Therefore, bits 3 and up only declare the descriptor table entry offset, while bit 2 specifies if this selector is a GDT or LDT selector (LDT - bit set, GDT - bit cleared), and bits 0 - 1 declare the ring level that needs to corespondcorrespond to the descriptor table entry's DPL field. If it doesn't, a General Protection Fault occurs; if it does corespondcorrespond then the CPL level of the selector used is changed accordingly.