Big-Endian and Little-Endian — Which Byte Comes First?

1. Split 0x12345678 into four bytes

The 32-bit hexadecimal value 0x12345678 consists of four bytes:

The leftmost byte, 12, is the most significant byte (MSB). The rightmost byte, 78, is the least significant byte (LSB). Endianness changes the order in which these bytes are placed in memory.

2. The same value looks different in memory

Both arrangements represent 0x12345678. When a CPU reads data in its native format, arithmetic results are unchanged. Byte order matters when bytes cross a boundary: a network connection, binary file, peripheral interface, or memory dump.

3. Endianness does not reverse the bits

Endianness normally describes the order of whole bytes. It does not reverse the bits inside each byte.

The written number itself does not change either. The logical value remains 0x12345678; only its byte-level representation in memory or a data stream changes.

4. Floating-point values become byte sequences too

The IEEE 754 single-precision representation of 1.0 has the 32-bit pattern 0x3F800000. The pattern is the same, but its bytes appear differently in memory.

If a sensor value or device register decodes into an implausibly large, tiny, or meaningless number, check the data type and the byte order.

5. Where byte order appears

• CPU memory:x86 and x64 systems generally use little-endian byte order.
• Networks:network byte order used by IP protocols is big-endian.
• Binary files:each file format defines its own byte order.
• Embedded systems:the CPU, protocol, and peripheral may use different conventions.
• Memory dumps:you need byte order to reconstruct values from displayed bytes.

Do not rely only on the CPU architecture. Check the specification for the particular data you are reading.

6. Identify the order from known data

A known value makes the order easy to spot. Store the 16-bit value 0x1234 and inspect two bytes from the lower address.

In a file or protocol specification, look for byte order, endianness, MSB first, or LSB first. “MSB first” can also refer to bit transmission order, so confirm whether the specification is discussing bytes or bits.

7. A practical checklist

1. How many bytes make up one value?
2. Does “first” mean the lowest address or the start of a data stream?
3. Does the MSB or LSB come first?
4. Is the value an unsigned integer, signed integer, or floating-point number?
5. Does the converted result fall within a realistic range?

Use M.A.L.'s converter when you want to inspect the relationship between hexadecimal and binary representations.

8. Remember it in one sentence