12. Segment Register Names

• All x86 segment registers are 16 bits in size, irrespective of the CPU:

  • CS, code segment. Machine instructions exist at some offset into a code segment. The segment address of the code segment of the currently executing instruction is contained in CS.

  • DS, data segment. Variables and other data exist at some offset into a data segment. There may be many data segments, but the CPU may only use one at a time, by placing the segment address of that segment in register DS.

  • SS, stack segment. The stack is a very important component of the CPU used for temporary storage of data and addresses. Therefore, the stack has a segment address, which is contained in register SS.

  • ES, extra segment. The extra segment is exactly that: a spare segment that may be used for specifying a location in memory.