Does my AMD-based machine use little endian or big endian?

Question

I'm going though a computers system course and I'm trying to establish, for sure, if my AMD based computer is a little endian machine? I believe it is because it would be Intel-compatible.

Specifically, my processor is an AMD 64 Athlon x2.

I understand that this can matter in C programming. I'm writing C programs and a method I'm using would be affected by this. I'm trying to figure out if I'd get the same results if I ran the program on an Intel based machine (assuming that is little endian machine).

Finally, let me ask this: Would any and all machines capable of running Windows (XP, Vista, 2000, Server 2003, etc) and, say, Ubuntu Linux desktop be little endian?

Thank You,
Frank

Answer 1

All x86 and x86-64 machines (which is just an extension to x86) are little-endian.

You can confirm it with something like this:

main() {
   int a = 0x12345678;
   unsigned char *c = (unsigned char*)(&a);
   if (*c == 0x78)
      printf("little-endian\n");
   else
      printf("big-endian\n");
}

Answer 2

In answer to your final question, the answer is no. Linux is capable of running on big endian machines like e.g., the older generation PowerMacs.

Answer 3

You have to download a version of Ubuntu designed for big endian machines. I know only of the PowerPC versions. I'm sure you can find some place which has a more generic big-endian implementation.

Answer 4

An easy way to know the endiannes is listed in the article Writing endian-independent code in C

const int i = 1;
#define is_bigendian() ( (*(char*)&i) == 0 )

Answer 5

"Intel-compatible" isn't very precise.

Intel used to make big-endian processors, notably the StrongARM and XScale. These do not use the IA32 ISA, commonly known as x86.

Further back in history, Intel also made the little-endian i860 and i960, which are also not x86-compatible.

Further back in history, the prececessors of the x86 (8080, 8008, etc.) are not x86-compatible either. Being 8-bit processors, endianness doesn't really matter...

Nowadays, Intel still makes the Itanium (IA64), which is bi-endian: normal operation is big-endian, but the processor can also run in little-endian mode. It does happen to be able to run x86 code in little-endian mode, but the native ISA is not IA32.

To my knowledge, all of AMD's processors have been x86-compatible, with some extensions like x86_64, and thus are necessarily little-endian.

Ubuntu is available for x86 (little-endian) and x86_64 (little-endian), with less complete ports for ia64 (big-endian), ARM(el) (little-endian), PA-RISC (big-endian, though the processor supports both), PowerPC (big-endian), and SPARC (big-endian). I don't believe there is an ARM(eb) (big-endian) port.

Answer 6

Assuming you have Python installed, you can run this one-liner, which will print "little" on little-endian machines and "big" on big-endian ones:

python -c "import struct; print 'little' if ord(struct.pack('L', 1)[0]) else 'big'"

Answer 7

Endianness White Paper from Intel Corp published November 15, 2004 http://www.intel.com/design/intarch/papers/endian.pdf

Contents
=========
Introduction .................................................5
Analysis     .................................................5
    Code Portability .........................................5
    Shared Data ..............................................5
    Best Known Methods .......................................5

Definition of Endianness .....................................5

Merits of Endian Architectures ...............................6
    Relevance of Endian Order ................................7

Byte Swapping ................................................8
    Byte Swapping Methods ....................................8
        Network I/O Macros ...................................8
        Custom Byte Swap Macros ..............................9
    Byte Swap Controls .......................................9
        Compile Time Controls ...............................10
        Run Time Controls ...................................10
    Recovering Byte Swap Overhead ...........................11

Platform Porting Considerations .............................11
    Data Storage and Shared Memory ..........................11
    Data Transfer ...........................................12
    Data Types ..............................................12
        Unions ..............................................12
        Byte Arrays .........................................12
        Bit Fields and Bit Masks ............................12
        Pointer Casts .......................................13
    Native Data Types .......................................14

Endian-Neutral Code .........................................14

Guidelines for Implementing Endian-neutral Code .............15
    Endian-neutral Coding Practices .........................15
    Code Analysis ...........................................15
        The Good ............................................16
        The Bad .............................................16
        The Ugly ............................................16

Converting Endian-specific to Endian-neutral Code ...........16

Reversing Endian-specific Architecture of Code ..............16

Conclusion ..................................................17