Page "X86 memory segmentation" Paragraph 17

In the 386 and later, protected mode retains the segmentation mechanism of 80286 protected mode, but a paging unit has been added as a second layer of address translation between the segmentation unit and the physical bus.

Also, importantly, address offsets are 32-bit ( instead of 16-bit ), and the segment base in each segment descriptor is also 32-bit ( instead of 24-bit ).

The general operation of the segmentation unit is otherwise unchanged.

The paging unit may be enabled or disabled ; if disabled, operation is the same as on the 80286.

If the paging unit is enabled, addresses in a segment are now virtual addresses, rather than physical addresses as they were on the 80286.

That is, the segment starting address, the offset, and the final 32-bit address the segmentation unit derives by adding the two are all virtual ( or logical ) addresses when the paging unit is enabled.

When the segmentation unit generates and validates these 32-bit virtual addresses from a program's logical ( 46-bit ) addresses, the enabled paging unit finally translates these virtual addresses into physical addresses.

The physical addresses are 32-bit on the 386, but can be larger on newer processors which support Physical Address Extension.