Little endian

From AMule Project FAQ
Jump to: navigation, search

Introduction to endianness

Having read the endianness article, you might already have an idea of what this is for.

The endianess defines the bytes' order in physical memory.


When you must store a two-bytes (or larger) value in memory, you can either store the first byte(s) in the first place or the second byte(s) in the first place.

Little endian defines that the first bytes will go first.


An example of a two-bytes number is 65534. This number requires two bytes to be stored in memory. The decimal number 65534 is represented, in hexadecimal, as FFFE (or 0xFFFE). Here we can see the two bytes: FF and FE.

We can decide wether we want to place the FF byte first in memory or the FE byte first.

Little endian tells us to place first the which whose numbers have less weight in the total number. That is FE, since FE here represents 254, while FF represents 65280.

So, physically in memory we would have:

Memory Graph:      |_____FE_____|_____FF_____|
Memory Possitions:     000001       000002


This endianness is used (amongst others) in x86, in AMD64 and in VAX machines.


To understand better the little endian concept it is helpful to compare it to the big endian concept.