really confused by mips target formats

["Eric Fisher" <joefoxreal at gmail dot com>]

Hi,
I really need your help. I'm confused by mips target formats. Here is
the function from tc-mips.c.

/* The default target format to use.  */

const char *
mips_target_format ()
{
  switch (OUTPUT_FLAVOR)
    {
    case bfd_target_aout_flavour:
      return target_big_endian ? "a.out-mips-big" : "a.out-mips-little";
    case bfd_target_ecoff_flavour:
      return target_big_endian ? "ecoff-bigmips" : ECOFF_LITTLE_FORMAT;
    case bfd_target_coff_flavour:
      return "pe-mips";
    case bfd_target_elf_flavour:
#ifdef TE_TMIPS
      /* This is traditional mips.  */
      return (target_big_endian
	      ? (HAVE_64BIT_OBJECTS
		 ? "elf64-tradbigmips"
		 : (HAVE_NEWABI
		    ? "elf32-ntradbigmips" : "elf32-tradbigmips"))
	      : (HAVE_64BIT_OBJECTS
		 ? "elf64-tradlittlemips"
		 : (HAVE_NEWABI
		    ? "elf32-ntradlittlemips" : "elf32-tradlittlemips")));
#else
      return (target_big_endian
	      ? (HAVE_64BIT_OBJECTS
		 ? "elf64-bigmips"
		 : (HAVE_NEWABI
		    ? "elf32-nbigmips" : "elf32-bigmips"))
	      : (HAVE_64BIT_OBJECTS
		 ? "elf64-littlemips"
		 : (HAVE_NEWABI
		    ? "elf32-nlittlemips" : "elf32-littlemips")));
#endif
    default:
      abort ();
      return NULL;
    }
}

Let's just talk about elf flavour. What are the traditional mips,
non-traditional mips and newabi? Why do both traditional mips and
non-traditional mips contain newabi?

Why does the object file assembled by mips-linux-as have elf32-tradbigmips
format? While one by mips-elf-as has elf32-bigmips?

Thanks.
Eric.