Segment Registers
1. 8086 addresses a segmented memory
2. Complete I MB memory is divided into 16 logical segments,
each of 64 KB.
3. There are 4 segment registers: Code Segment (CS), Data
Segment (DS), Extra Segment (ES) and Stack Segment (SS).
4. Segment Registers hold the offset address of the respective
segments.

• 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.