A sequence of bytes.

A byte is a chunk of eight bits. For example, the letter j is usually represented as the byte 01101010, and the letter k is 01101011.

Seeing each byte as a stream of zeros and ones can be quite confusing though, so it is common to use hexidecimal numbers instead:

| Binary | Hex |
+--------+-----+
|  0000  |  0  |
|  0001  |  1  |
|  0010  |  2  |
|  0011  |  3  |     j = 01101010
|  0100  |  4  |         \__/\__/
|  0101  |  5  |           |   |
|  0110  |  6  |           6   A
|  0111  |  7  |
|  1000  |  8  |     k = 01101011
|  1001  |  9  |         \__/\__/
|  1010  |  A  |           |   |
|  1011  |  B  |           6   B
|  1100  |  C  |
|  1101  |  D  |
|  1110  |  E  |
|  1111  |  F  |

So j is 6A and k is 6B in hexidecimal. This more compact representation is great when you have a sequence of bytes. You can see this even in a short string like "jazz":

binary                                 hexidecimal
01101010 01100001 01111010 01111010 => 6A 61 7A 7A

Anyway, the point is that Bytes is a sequence of bytes!

Different computers store integers and floats slightly differently in memory. Say we have the integer 0x1A2B3C4D in our program. It needs four bytes (32 bits) in memory. It may seem reasonable to lay them out in order:

   Big-Endian (BE)      (Obvious Order)
+----+----+----+----+
| 1A | 2B | 3C | 4D |
+----+----+----+----+

But some people thought it would be better to store the bytes in the opposite order:

  Little-Endian (LE)    (Shuffled Order)
+----+----+----+----+
| 4D | 3C | 2B | 1A |
+----+----+----+----+

Notice that the bytes are shuffled, not the bits. It is like if you cut a photo into four strips and shuffled the strips. It is not a mirror image. The theory seems to be that an 8-bit 0x1A and a 32-bit 0x0000001A both have 1A as the first byte in this scheme. Maybe this was helpful when processors handled one byte at a time.

Most processors use little-endian (LE) layout. This seems to be because Intel did it this way, and other chip manufactures followed their convention. Most network protocols use big-endian (BE) layout. I suspect this is because if you are trying to debug a network protocol, it is nice if your integers are not all shuffled.

Note: Endianness is relevant for integers and floats, but not strings. UTF-8 specifies the order of bytes explicitly.

Note: The terms little-endian and big-endian are a reference to an egg joke in Gulliver's Travels. They first appeared in 1980 in this essay, and you can decide for yourself if they stood the test of time. I personally find these terms quite unhelpful, so I say “Obvious Order” and “Shuffled Order” in my head. I remember which is more common by asking myself, “if things were obvious, would I have to ask this question?”