Why did BSD/OS switch to ELF?
The main reason for switching to ELF was to implement dynamic linking. A number of third-party suppliers and customers had requested this feature. Dynamic linking allows programs to delay the mapping of names in program sources (`symbols’) to code or variables inside libraries until the program runs. This delayed mapping makes it easy to change shared libraries without affecting the programs that use them. Since so many other unix-like systems use ELF, we also expect to benefit from the development that is going into ELF tools. And ELF representations are richer than the traditional a.out file representations, so we have more flexibility in the way that we can build executable files.
