Htonl - "Bit Endianness"

"Bit Endianness"

The terms bit endianness or bit-level endianness are seldom used when talking about the representation of a stored value, as they are only meaningful for the rare computer architectures where each individual bit has a unique address. They are used however to refer to the transmission order of bits over a serial medium. Most often that order is transparently managed by the hardware and is the bit-level analogue of little-endian (low-bit first), although protocols exist which require the opposite ordering (e.g. Teletext, I²C, and SONET and SDH). In networking, the decision about the order of transmission of bits is made in the very bottom of the data link layer of the OSI model. As bit ordering is usually only relevant on a very low level, terming transmissions "LSB first" or "MSB first" is more descriptive than assigning an endianness to bit ordering.

Bit endianness is also used when referring to certain image formats, particularly bitonal images, which store a series of pixels as individual bits within a byte. If the bit order is incorrect, every group of eight pixels in the image will appear backwards.