With a big endian approach, the most significant part of the number is stored first, and in a little endian format, the least significant part of the number is stored first in memory.
Essentially, big endian and little endian formats read in different directions. For example, the hexadecimal number 7A0516 would be represented in big endian format as 7A0516. In little endian format, though, it would be presented as 16057A.
The term endianness refers to the use of either a big endian or a little endian format. Most new processors use a little endian format, while technologies like TCP/IP and JPEG use a big endian format.
In general, consumer technologies and broader protocols tend to use a big endian format, while many new processors use little endian format. In a little endian approach, the first or leftmost numbers stay the same as the amount of memory used to store the number grows. However, a big endian format allows for reading the most significant value of the number first, which can have its own use.
It comes down to this: Humans, experts point out, read in a big endian format, while computers benefit from reading in a little endian format. That's much of the difference, and a reason why big endian format is still used (in addition to the legacy issue) even though many consider it mostly a legacy format that's being changed over to little endian over time.
In terms of facilitating a switch between the two formats, some advocate using byte swaps to emulate big endian format for little endian inputs (or to change to little endian for the sake of a new chip). In terms of understanding in a network layer whether a certain system uses big endian or little endian format, it’s observed that “application layer protocols dictate their own endianness.”
The bottom line is that it's good for engineers and coders and others to have a well-rounded idea of how endianness works in modern systems.
Interestingly, the terms big endian and little endian are often attributed to the book “Gulliver's Travels” by Jonathan Swift, where different groups of people like to crack eggs on either the big or the little end.