11. Segment Registers in Real Mode

• The 8088, 8086, and 80286 CPUs have four segment registers to hold segment addresses.

• The 386 and later CPUs have two more, also available in real mode.

• Note: the 386 and later Intel x86 CPUs still use 16-bit size segment registers.

• Each segment register is 16-bit in size.

• No matter how location in memory is accessed, the segment address of that location must be present in one of the six segment registers:

  • CS,  DS,  SS,  ES,  FS  and  GS.