Descriptor Tables

There are three tables which hold descriptors.

The three tables are:

The Global Descriptor Table or GDT, describes memory objects which are accessible to all processes.

The GDT is located by means of a hardware register called the GDTR which contains the linear address and length of the GDT.

The Local Descriptor Table or LDT, describes memory objects which are unique to one process or are shared among a few processes by design.

The LDT is located by means of a hardware register called the LDTR which contains a selector. The descriptor referenced by this selector must be a system descriptor which describes an LDT.

The Interrupt Descriptor Table or IDT, has gates that specify interrupt handler entry points.

The IDT is located by means of a hardware register called the IDTR which contains the linear address and length of the IDT. The interrupt number is used to index into this table when an interrupt occurs.

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