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Hello every one
I have a little question about the hiden part of segment register that i wish that you help me
How much i should reserve in memory in order to store a segment register the tow part hidden and visible parts using Mov instruction and did Mov store the Hidden part .
Thank you .

You can't retrieve the hidden part of a segment register using conventional means. You'd need a SMM handler or virtual machine for that. (The virtual machine being the only context where this action actually makes sense)

To be more specific about Combuster's answer: 2 bytes and no.