In wiki, "big-endian" refers to the storage order of multiple bytes.
And a byte consists of 8 bits, it's also important to note the order of these bits.
dd if=/dev/sda count=1 | xxd -b, and found out that bytes are stored in the opposite increasing direction of address:
01100011 (lower address is on the left, while this byte is ascii character'c')
It seems to be a bit-level "big-endian".
how to explain this odd phenomenon?