One of the very early union file systems is Clearcase by Rational Software (now owned by IBM). A workspace is put together via a series of views (which are versioned software releases) overlaid upon one another. The software required modifying the Solaris Kernel and required very powerful CPUs to work well. You would make all your changes in the top layer and when it was time to commit you only had to specify what branch(es) to add those changes to - clearcase knew what had been changed. en.wikipedia.org/wiki/Rational_Cle... .
One of the very early union file systems is Clearcase by Rational Software (now owned by IBM). A workspace is put together via a series of views (which are versioned software releases) overlaid upon one another. The software required modifying the Solaris Kernel and required very powerful CPUs to work well. You would make all your changes in the top layer and when it was time to commit you only had to specify what branch(es) to add those changes to - clearcase knew what had been changed.
en.wikipedia.org/wiki/Rational_Cle... .
That's interesting, I did not know that! Thanks for sharing it :)