1.1 UNIX

a powerful benefit of UNIX compliance is that source code, if carefully written, can be ported across platforms. Adhering to the POSIX standard (a.k.a. IEE std 1003.1-2001) ensures such compatibility even with non fully compliant systems (e.g., WSL). Binary compatibility, however, is impossible due to the different binary format (mach-O), and different numbering.

Why does different numbering interfere with binary compatibility?

Because compiled executables embed specific numeric identifiers—like system‐call numbers, library symbol ordinals, and error codes—that vary between platforms, a Mach-O binary’s hard-coded numbers won’t correspond to the correct routines on a system with a different numbering scheme, preventing compatibility.