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Memory Segmentation of Intel 8086

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Memory Segmentation

The total memory size is divided into
segments of various sizes.
A segment is just an area in memory.
The process of dividing memory this
way is called Segmentation.
In memory, data is stored as bytes.
Each byte has a specific address.
Intel 8086 has 20 lines address bus.
With 20 address lines, the memory that can
be addressed is 220 bytes.
220 = 1,048,576 bytes (1 MB).
8086 can access memory with address
ranging from 00000 H to FFF H.

Segment Registers

Each of these segments are addressed by
an address stored in corresponding
segment register.
These registers are 16-bit in size.
Each register stores the base address
(starting address) of the corresponding
segment.
Because the segment registers cannot
store 20 bits, they only store the upper 16
bits.

Max. Size of Segment

All offsets are limited to 16-bits.
It means that the maximum size
possible for segment is 216 = 65,535
bytes (64 KB).
The offset of the first location within the
segment is 0000 H.
The offset of the last location in the
segment is FF H.