Page "X86 memory segmentation" Paragraph 2

In real mode, the 16-bit segment selector is interpreted as the most significant 16 bits of a linear 20-bit address, called a segment address, of which the remaining four least significant bits are all zeros.

The segment address is always added with a 16-bit offset to yield a linear address, which is the same as physical address in this mode.

For instance, the segmented address 06EFh: 1234h has a segment selector of 06EFh, representing a segment address of 06EF0h, to which we add the offset, yielding the linear address 06EF0h + 1234h = 08124h ( hexadecimal ).