What are the segment and offset in real mode memory addressing?

Question

I am reading about memory addressing. I read about segment offset and then about descriptor offset. I know how to calculate the exact addresses in real mode. All this is OK,

Answer 1

Under x86 Real-Mode Memory the physical address is 20 bit long and is calcolated:

PhysicalAddress = Segment * 16 + Offset

Check also: Real-Mode Memory Management