What is the purpose of CS and IP registers in Intel 8086 assembly?

x86 intel x86-16
idjuradj picture idjuradj · Jul 21, 2013 · Viewed 66.1k times · Source

So, as the question states, what is the purpose of CS and IP registers in intel's 8086

I found this explanation:

Code segment (CS) is a 16-bit register containing address of 64 KB segment with processor instructions. The processor uses CS segment for all accesses to instructions referenced by instruction pointer (IP) register. CS register cannot be changed directly. The CS register is automatically updated during far jump, far call and far return instructions.

and this for IP:

Instruction Pointer (IP) is a 16-bit register.

I don't really understand what this basically means, so if someone could provide a more "vivid" explanation, that would be great :)

Answer

kiran james picture kiran james · Apr 6, 2014

The physical address is calculated from 2 parts. i) segment address. ii) offset address. The CS(code segment register) is used to address the code segment of the memory i.e a location in the memory where the code is stored. The IP(Instruction pointer) contains the offset within the code segment of the memory. Hence CS:IP is used to point to the location (i.e to calculate the physical address)of the code in the memory.

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