Question

What is the maximum allowable size for memory segment in 8086?

Answer 1

The 8086 segment registers are 16-bit therefore there can be 65536 segments - but they overlap. The 20-bit physical address is obtained by shifting the segment register left 4 bits and adding the address offset. That means a segment may start at any 16-byte alignment. From the overlap it follows that there are many ways to addess one memory location, for example 0000:0010and 0001:0000 address the same location.

Because the address offset is also 16 bits, the addressable size of any segment is 65536 bytes. So the maximum size of a segment is 65536 bytes, and the smallest is 16 bytes - though on the 8086 the entire segment may be read/written with no protection.

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