endianness

Multi-byte data (16-bit, 32-bit, 64-bit numbers) must be stored in memory as individual bytes. But which byte goes at the lowest memory address — the most significant or least significant byte?

Endianness defines the byte order used to store multi-byte data in memory: Big Endian puts the Most Significant Byte first; Little Endian puts the Least Significant Byte first.

1. A 32-bit number like 0x12345678 has 4 bytes: 0x12 (MSB), 0x34, 0x56, 0x78 (LSB)
2. Big Endian stores: 12 34 56 78 at increasing memory addresses
3. Little Endian stores: 78 56 34 12 at increasing memory addresses
4. When reading multi-byte data, CPU must know the correct byte order
5. Mismatch between systems causes data corruption (e.g., network data on x86)

• Big Endian: matches human reading order (easier to debug in memory dumps)
• Little Endian: more efficient for CPU arithmetic (LSB processed first on x86)
• Network protocols use Big Endian (called “network byte order”)
• Intel x86/AMD use Little Endian; some RISC chips use Big Endian

• Built from: Memory, Multi-Byte Data
• Contrasts with: Big Endian vs Little Endian — different byte orders
• Related: Network Byte Order, Memory Address
• Builds into: Data Serialization — must handle endianness when transferring data

• Endianness only matters for multi-byte data (byte-order sensitive)
• Single bytes are not affected by endianness
• Mixing systems with different endianness causes data corruption
• Some CPUs are bi-endian (can switch mode) — software must track current mode