Some computer architectures number bytes in a binary word from left to right, which is referred to as

big-endian. 

Other architectures number the bytes in a binary word from right to left, which is referred to as little-endian.

Using big-endian and little-endian methods, the number 0x12345678 would be stored as shown in the following table.

 

Byte order	Byte 0	Byte 1	Byte 2	Byte 3
Big-endian	0x12	0x34	0x56	0x78
Little-endian	0x78	0x56	0x34	0x12

例子：

下面C# code中有2个txt文件：LittleEndian.txt和BigEndian.txt，他们包含相同的文本内容:都是aa，但不同的编码方式，分别是UCS-2 Little Endian 和UCS-2 Big Endian.

示例中先分别用二进制的方式读出文件中的内容；再用StreamReader读出文件的内容

static void Main(string[] args)        {            byte[] leBytes = ReadAsBinary(".\\LittleEndian.txt");            Console.WriteLine("Little Endian:");            PrintByteArray(leBytes);            Console.WriteLine();            byte[] bigBytes = ReadAsBinary(".\\BigEndian.txt");            Console.WriteLine("Big Endian:");            PrintByteArray(bigBytes);            Console.WriteLine();            byte[] srByes;            using (StreamReader reader = new StreamReader(".\\LittleEndian.txt", true))            {                srByes = Encoding.Unicode.GetBytes(reader.ReadToEnd());            }            Console.WriteLine("StreamReader Little Endian:");            PrintByteArray(srByes);            Console.WriteLine();}        private static byte[] ReadAsBinary(string path)        {            FileStream fs = new FileStream(path, FileMode.OpenOrCreate, FileAccess.Read);            BinaryReader breader = new BinaryReader(fs);            byte[] bytes = breader.ReadBytes(6);            return bytes;        }

输出：

结论：

UCS-2 Little Endian编码的文件，其内容以FFFE开头；

UCS-2 Big Endian编码的文件，其内容以FEFF开头；