“In all modes except for long mode, each segment register holds a selector, which indexes into either the GDT or LDT. That yields a segment descriptor which, am

“In all modes except for long mode, each segment register holds a selector, which indexes into either the GDT or LDT. That yields a segment descriptor which, among other things, supplies the base address and extent of the segment.” A tad inaccurate. In 16-bit real mode the segment registers are used directly in the addressing scheme by specifying the 64kb segment (16-byte aligned) that we’re working in.