Answer Posted / shabir gojree lpu, jalandhar
The segment register in the 80806/8088 microprocessor
contains the base address (divided by 16) of a region of
memory. Since the register is 16 bits in size, there are
65,536 possible segment base addresses, ranging from 00000H
to FFFF0H, in increments of 00010H.
After address translation at the instruction level, the
generated 16 bit offset is added to the selected segment
register times 16 to generate a physical address between
00000H and FFFFFH. (If the offset and base go past FFFFFH,
they wrap around back to 00000H.) Since the offset is also
16 bits in size, and since the overlap is only 4 bits
(times 16), then each 64 kb segment overlaps by 16 bytes.
There are four segment registers; CS, DS, ES, and SS,
standing for Code Segment, Data Segment, Extra Segment, and
Stack Segment.
CS is used for opcode fetches. DS is used for normal data.
ES is used for certain string operations as the destination
address. SS is used for stack and frame (BP) data.
The segment registers can be implicitly selected by
context, or they can be explicitly selected with a segment
prefix opcode.
| Is This Answer Correct ? | 8 Yes | 3 No |
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