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Recall that 8086 and 8088 CPUs had 20 address pins, limiting a program to 1 megabyte of memory.
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To express a 20-bit address, two 16-bit registers are used:
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segment address in one 16-bit register,
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and the offset address in another 16-bit register.
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The memory location of a particular byte from one megabyte of memory is calculated as
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segment start address
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plus distance between the byte and the segment start.
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The byte's distance from the start of the segment is referred to as the byte's offset address.
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SEGMENT:OFFSET addresses are always written in hexadecimal notation.
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For example, an address of one byte of data MyByte is given as 0001:001D.
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This means that MyByte is in segment 0001H and is located 001DH bytes from the start of that segment.
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Since segments can overlap, same byte could also be located by SEGMENT:OFFSET combinations 0002:000D or 0001:001D.
