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?

Solution 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:

#include <stdio.h>
int main() {
    int a = 0x12345678;
    unsigned char *c = (unsigned char*)(&a);
    if (*c == 0x78) {
       printf("little-endian\n");
    } else {
       printf("big-endian\n");
    }
    return 0;
}

Solution 2

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 )

Solution 3

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'"

Solution 4

"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.

Solution 5

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.

View more solutions

Comments

[Frank V]

Is that distribution, that I linked to, able to run on big endian. Thank you for address that part of my question.

[mnuzzo]

I think they're asking if those operating systems can run on little endian machines, which they can. In fact, I think they have to make special versions for the older generation PowerMacs because the PowerPC architecture is big-endian.

[Mark]

Now that Ubuntu has ARM support, its possible for "Ubuntu" to run on a big endian processor. Recent ARM cores can run in either little or big endian mode.

[ephemient]

Ubuntu's second class ports include ia64, armel, hppa, powerpc, and sparc. In earlier releases, PowerPC was a first class port, and there was one release where SPARC was up there too.

[Frank V]

Wow, thank you for the detail. This is great support information.

[Jarosław Bielawski]

Two minor corrections: endianness matters also for 8 bit processors as some instructions refer to 16 bit quantities like addresses (LDA $1234 (loading a byte from address $1234) will be coded AD 34 12 on the 6502. And AMD did have another architecture than x86 it was the 29000 series RISC processors that was very popular in embedded designs like laser printers.

[ephemient]

@tristopia Thanks for the info, I wasn't aware of all of that.

[GMasucci]

PowerPC are bi-endian: that is they can run in big or little endian mode - see here - just fore completeness of information. Cheers

[Peter Cordes]

Cool, but this question isn't actually about how to determine / detect endianness at compile time. There's very likely another Q&A where this would be more useful. (A comment on this question with a link to such a Q&A would be good.)

[Jiminion]

Linux also runs/ran on MC68K (68000, 68010, etc.) processors, which are little endian.