This article is surprisingly better (and longer ;) than I expected, but it skipped over explaining one important distinction; "ELF" is an executable file format

This article is surprisingly better (and longer ;) than I expected, but it skipped over explaining one important distinction; "ELF" is an executable file format, but "a.out" is more than just a default file name; it's also the name of a totally different executable file format. Originally, the "a.out" executable format, and hence, the "a.out" file name were due to being the "assembler output" of Ken Thompson's assembler in 1968. Most all UNIX-based systems have moved to using newer ELF format, but there are a few hold-outs still using the older a.out format. As for why ELF formatted executable files are still given the file name "a.out" by default, even when they are not in the "a.out" executable format, it's just a historic artifact (or annoyance) due to compilers and linkers. http://en.wikipedia.org/wiki/A.out http://en.wikipedia.org/wiki/A.out