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Store-ordering in memory: big endian and littel endian

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• Store ordering
  • When more than 1 bytes in a register is stored in memory, there are 2 store orderings possible:

    Big endian ordering where the most-significant byte is stored first: Little endian ordering where the least-significant byte is stored first:

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  • The endianness in use is determined by the CPU type.

    For example:

    The INTEL processors (x86) are little endian The ARM processor is little endian by default; and can be programmed to operate as big endian Many older processors were big endian, such as: Motorola M68000 and SPARC

    Endianness is initially an arbitrary decision by the semiconductor vendor that can have a long-term impact on a line of products.

    When vendors update their technology, they keep the existing endianness to help maintain backward compatibility.

    For example, the designers of the Motorola 68000 and the Intel 8086 (predecessor of the x86 family) chose their endianness in the 1970s and continue to use their respective endianness today.

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• Which ordering is better ?
  • The ordering has absolutely no effect of processor performance and any other performance factor.

    As long as the processor retrieve the bytes stored in the memory in the same ordering as the processor stores the bytes, the load and store instructions will operate correctly and with the same efficiency

    In fact, the term Big endian and Little endian is taken from the book Gulliver's travels and describes a meaningless squabble between 2 faction in the nation Lilliput:

    The Big-Endians, who broke their boiled eggs at the big end, rebelled against the king, who demanded that his subjects break their eggs at the little end.

    The people in Lilliput were very tiny (compared) to Gulliver and their eggs is even smaller.

    Gulliver can't tell which end was the big end and which was the little end. So to Gulliver, this squabble was meaningless...

    So it does not matter which store-ordering a processor uses...

    See: click here

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• ARM's processor store ordering
  • The ARM processor uses little endian (by default)

    (We did not change the default.)

    That's why you had to reverse the byte ordering in this webpage: click here