What is the difference between the Linux distros?

Question

What is the difference between the several GNU/Linux distros like Ubuntu and Fedora? Before brickbats fly for asking an oft repeated question, I am talking of differences related to the internal working of the operating system, not eye candy, desktop environments, package managers, ease of use and other user interface related features.

To be more specific, suppose I am purely interested in the performance of a certain C++ program (serial or parallel) that I have written. Say I have Ubuntu and Fedora installed on the same desktop machine, with both having the same Linux kernel version, will the program performance be the same on both the operating systems?

A related question would be why some Unix like OS'es like FreeBSD (which is not a GNU/Linux distro) are more favored for server platforms than others.

Answer 1

The internal differences, excluding package systems and GUI, are few, and quite all of them not so relevant for what you are asking.

The only relevant thing for your C++ programs is the version of the kernel and/or the version of the libraries your program is linked against, that somewhat depends on the distro you choose, but you can always replace them by downloading and compiling the sources (if pre-built packages are not available).

The performance difference will be, assuming you're sticking on the same machine and even with different libraries, almost undetectable, excluding statistical noise (if the distro is GUI based, for example, then some GUI-related job can randomly interleave with your C++ program causing it to do a bad benchmark, occasionally - yeah, even on multicore machines). If you are aiming at performance, and predictability (low variance on the execution time) then avoid GUI based distros and stop any service that can occasionally do some job that interleaves with your program (e.g. networking).