[Zev]

A "Universal Binary" is the exact same thing as a "Fat Binary," the only difference is that marketing gave it a new name.

If you look at the mach-o header of a binary that contains multiple architectures (initially, ppc/68k or now, i386/x86_64/ppc), the first 8 bytes will be either 0xcafebabe or 0xbebafeca, depending on your endianness. These values are also #define'd as FAT_MAGIC or FAT_CIGAM in <arch/fat.h>.

If you're on a Mac, you can check this by typing `open -h fat.h` into a Terminal and opening up the binary of a universal app in a hex editor.

[jonah]

Yep. But I don't believe the 68k/PPC ones were called "Universal Binary".

[Zev]

If it walks like a duck and quacks like a duck...

Please see the end of the first line in my previous post: ...the only difference is that marketing gave it a new name.