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IBM PC case -----------

Suppose we need to create a segment occupying addresses F000:1000..F000:2000 Let's calculate linear addresses:

        start = (0xF000 << 4) + 0x1000 = 0xF1000
        end   = (0xF000 << 4) + 0x2000 = 0xF2000
The segment base must be selected so that the first offset in our segment will be 0x1000. Let's find it using the following equation:
        VirtualAddress = LinearAddress - (SegmentBase << 4);
        0x1000         = 0xF1000 - (base << 4);
After solving this equation, we see that the segment base is equal to 0xF000. (you see, this is really a very simple case :) )

Now, we can create a segment entering:

        segment start address:  0xF1000
        segment end address:    0xF2000
        segment base:           0xF000
Please note that the end address never belongs to the segment in IDA.

Go back to addressing space concepts

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