Segment Addressing
For more details on this topic, see X86 memory segmentation.In real mode each logical address points directly into physical memory location, every logical address consists of two 16 bit parts: The segment part of the logical address contains the base address of a segment with a granularity of 16 bytes, i.e. a segments may start at physical address 0, 16, 32, ..., 220-16. The offset part of the logical address contains an offset inside the segment, i.e. the physical address can be calculated as physical_address : = segment_part × 16 + offset (if the address line A20 is enabled), respectively (segment_part × 16 + offset) mod 220 (if A20 is off) Every segment has a size of 216 bytes.
Read more about this topic: Protected Mode, Features
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