I am so happy to see that this correct explanation has finally spread.
When I first started posting on HN the standard response you would get was the retcon explanation like the parent comment or even more nonsensical ones like "usr == UNIX system resources".
At the time cursory searching could not find any actual explanations for this. I started a deep dive into Usenet history and reaching out to folks who knew the history, looking for scraps of info in old Unix books, etc and found the correct explanation as you posted. It was entirely an ad hoc solution to running out of disk space. /usr got moved to the second disk. When root got full again they moved some large binaries to /usr/bin. When the /usr disk got full the user home directories were the easiest thing to move so they moved to /home on a third disk. Every other explanation is purely post-hoc rationalization.
Since then I've been pointing it out when the topic comes up and I am happy that general knowledge of the actual history has started to spread.
Note: I am not taking credit for this, many other people have been correcting the story both before and after me. I'm just glad the true story is seeping into the collective tech community. Sometimes misinformation or incorrect "facts" seem to linger no matter how many times and how many people correct them... but this makes me hopeful that misinformation can be corrected.
When I first started posting on HN the standard response you would get was the retcon explanation like the parent comment or even more nonsensical ones like "usr == UNIX system resources".
At the time cursory searching could not find any actual explanations for this. I started a deep dive into Usenet history and reaching out to folks who knew the history, looking for scraps of info in old Unix books, etc and found the correct explanation as you posted. It was entirely an ad hoc solution to running out of disk space. /usr got moved to the second disk. When root got full again they moved some large binaries to /usr/bin. When the /usr disk got full the user home directories were the easiest thing to move so they moved to /home on a third disk. Every other explanation is purely post-hoc rationalization.
Since then I've been pointing it out when the topic comes up and I am happy that general knowledge of the actual history has started to spread.
Note: I am not taking credit for this, many other people have been correcting the story both before and after me. I'm just glad the true story is seeping into the collective tech community. Sometimes misinformation or incorrect "facts" seem to linger no matter how many times and how many people correct them... but this makes me hopeful that misinformation can be corrected.