If you are like me, trying to create a library of tech knowledge on a digital platform which can survive a serious disaster, then this site is for us:
https://www.geekbooks.me/Note, Book published in 2011 an earlier are free downloads (PDF's). More recent books require a "premium" subscription.
Since older books still have a VAST amount of useful information, you DO NOT really need to buy the advanced subscription...
The total library is around 70-80 Gigabytes, which can fit on the larger USB Flash drives...
You may download individual books in PDF format
Without the "premium" subscription, there is a 5 book daily limit downloads. I can live with this.