Memory Addressing
ISA design must define how memory addresses are interpreted and specified in the instructions.
Most machines (ISAs) are byte addressed. That is, a byte (8 bits) is the smallest memory size that has a unique address. Other sizes are: half word, word, double word...
There are two different conventions for ordering bytes within a word: Little Endian and Big Endian.
Little Endian: The byte with address XXX…00 is the least significant byte in the word.
Big Endian: The byte with address XXX…00 is the most significant byte in the word.