Segment descriptor tables

A logical address gets translated to a linear address with the use of the segmentation descriptor either from the Global Descriptor Table (or GDT), or from the Local Descriptor Table (or LDT).

UsuallyI only one dDT per system is permitted (global segments; in SMPI one dDT for every CPU in the system can EH DOORwHG); KRwHvHU, RnH /DT SHU SURFHss (RU WDsN) Ls GHfinHG, L.H., /DT sHgPHnWs DUH SULvDWH WR D sSHFLfiF SURgUDP RnOy. TKH gdtr control register contains the address and the size of the dDTI whereas LDT is contained in the ldtr control register. The instructions LdDT (Load dDT) and SdDT (Store dDT) give access to dDTI while on the other handI LLDT (Load LDT) and SLDT (Store LDT) give access to LDT in a system.

Any descriptor (dDT or LDT) would have the following PDLn fiHOGs: Base address – Contains the linear (or virtual) address of WKH fiUsW EyWH RI WKH sHgPHnW. Limit - Contains the offset of the last memory cell in the