> For example system with ELF could not run at 4MB of ram without extreme swapping, but a.out (like Slackware 3.9 AFIK) could without much problems.

> I never understood why a.out binaries went out of fashion :(

Storage was expensive. The promise of ELF was shared libraries. The idea was that a lot of libraries are used by a lot of programs so splitting the code between the main program and the shared library is a good thing.

The idea has not lived to its promise. Shared libraries in OSS are tending to became a DLL hell. There are also a lot of libraries with duplicated functionality which makes things even worse.

> Fun fact: older versions of Slackware were using EGCS instead of GCC compilers.

This was a good thing. Just like today with llvm. GCC was resting in its 7 day and nobody bothered to update it for the new stuff. Then EGCS came out and gave GCC a kick in the butt, helping to continue.