Amazing that how much basic knowledge society is leaving behind - it never is needed for the common guy and so we never know it. To that extent this is a huge first step in preserving those "long forgotten" bits. Ironically this relies on world's communication systems being intact and no one person knows how it all works end to end! Someone should do a similar archive for world's commonly used communication systems.…
I use a computer every day, but I wouldn't know where to start to rebuild one from scratch. There are books like "Linux from scratch", but it is far from enough: we would need to "re-invent" electricity, silicon, assembly languages, operating systems... With the division of labour, nobody has the knowledge to build all this.
I think it would take centuries to re-create what we have now. The cool thing is, we wouldn't need to care about backward compatibility / legacy apps, and we could skip C++ and immediately standardize on Lisp ;)