One base and one index register is used in this addressing mode. The value of the base register and the index register are added together to get the effective address. For example “mov [bx+si], ax” moves the word contained in the AX register to offset attained by adding BX and SI in the current data segment. The instruction “mov [bp+di], al” moves the byte contained in AL to the offset attained by adding BP and DI in the current stack segment. Observe that the default segment is based on the base register and not on the index register. This is why base registers and index registers are named separately. Other examples are “mov [bx+di], ax” and “mov [bp+si], ax.” This method can be used to access a two dimensional array such that one dimension is in a base register and the other is in an index register.
Base + Index + Offset
This is the most complex addressing method and is relatively infrequently used. A base register, an index register, and a constant offset are all used in this addressing mode. The values of the base register, the index register, and the constant offset are all added together to get the effective address. For example “mov [bx+si+300], ax” moves the word contents of the AX register to the word in memory starting at offset attained by adding BX, SI, and 300 in the current data segment. Default segment association is again based on the base register. It might be used with the array base of a two dimensional array as the constant offset, one dimension in the base register and the other in the index register. This way all calculation of location of the desired element has been delegated to the processor. 
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