User:New16
Endianness refers to the order in which bytes of a multi-byte structure are placed to main memory (RAM). The bit order in any byte is normally from bit seven downto bit zero and remains preserved.
Big- vs. little-endian
In big-endian the most-significant (left-hand) byte, in little-endian the least-significant (right-hand) byte is stored at the lowest address.
| Memory address |
n | n+1 | n+2 | ... | ||
|---|---|---|---|---|---|---|
| Value 0x15 |
Big-endian: | 0x15 | - | - | - | |
| Little-endian: | 0x15 | - | - | - | ||
| Value 0x0A15 |
Big-endian: | 0x0A | 0x15 | - | - | |
| Little-endian: | 0x15 | 0x0A | - | - | ||
| Value 0x780A15 |
Big-endian: | 0x78 | 0x0A | 0x15 | - | |
| Little-endian: | 0x15 | 0x0A | 0x78 | - | ||
| a.s.o. | ||||||
Little-endian may seem unlogical until you consider that a variable can be used more easily as both 8-bit, 16-bit, 32-bit or even 64-bit without changing its base address. Therefor AMD and Intel use little-endian order.
Example
Let's assume a x86-computer, which means little-endian order. Register eax contains the value 0xCAFEF00D. You store this register at address 0.
Common CPUs
| CPU | Endianness |
|---|---|
| x86 | little |
| x86-64 | little |
| MIPS | both |
| Motorola | big |
| 68k | big |
| PowerPC | both |