I mean it's no problem in Win, but in Linux it's sometimes impossible to install new programs if you didn't update the whole OS. And if you didn't update it for a long time then you have to do several updates in a row which is very time-consuming and sometimes unaffordable. Why can't I update the OS from a several releases older version to the newest. And also often I encounter old programs that require older versions of libs. Why can't I separately install older libs for such cases? I know that there are distros that can solve these problems. But they are unpopular and have too little documentation and packages and too unstable and raw. And why are such distros so raw and unpopular?
closed as unclear what you're asking by strugee, slm♦, Karlson, Anthon, jasonwryan Apr 17 '14 at 19:39
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You ask quite a lot of questions here. You are supposed to ask one question. However...
Why most distros' package managers don't allow the same package in multiple versions
In some cases they do. Eg. Debian allows different versions of Python to be installed simultaneously. In most cases they do not, because it would require extra overhead, some level of technical difficulty, and it is not usually necessary to have multiple versions of a package installed simultaneously. The main issue is that the names of the files will collide, since most packages are not designed to be installed simultaneously in different versions. Therefore such files need to have different paths for each version of the package.
and newest versions without upgrading?
This is unclear. I assume you mean installing newer versions of packages without upgrading the entire OS. Sure you can. Debian has backports, and other distributions presumably have similar concepts. Or you can do a backport yourself.
Why can't I update the OS from a several releases older version to the newest.
Because it is very difficult to support all these different upgrade options. Supporting an upgrade from version n to version n+1 is hard enough.
And also often I encounter old programs that require older versions of libs. Why can't I separately install older libs for such cases?
Sure you can. Who says you can't?