The GNU assembler can be configured to produce several alternative
object file formats. For the most part, this does not affect how you
write assembly language programs; but directives for debugging symbols
are typically different in different file formats. See section Symbol Attributes.
On the machine specific, as can be configured to produce either
a.out or COFF format object files.
On the machine specific, as can be configured to produce either
b.out or COFF format object files.
On the machine specific, as can be configured to produce either
SOM or ELF format object files.