> One copy in memory can serve millions on your website.

But they have to download it, and you might not have the bandwidth to service millions of downloads in less than a few hours ….

A million copies of a 10MB PDF is 10 terabytes. A gigabit internet connection could serve that in 22 hours. Pretty straightforward to do that.

If you go the sponsored route and use a CDN, then at 10 TBit/second it would only take 18 hours to serve it 8 billion times (approx once for every human). But there's still bittorrent and if the file's popular, that gigabit upload won't be the limiting factor.

> A million copies of a 10MB PDF is 10 terabytes. A gigabit internet connection could serve that in 22 hours. Pretty straightforward to do that.

Yes, just so. The parent seemed to be arguing that it was too much to claim that it would take a few hours. I'd definitely call 22 hours at least a few!

That was at 10 MB per book, but that seems pretty high. Looking at the most popular books at Project Gutenberg suggests that 0.5 to 1.5 MB is where most fall.

Thanks for the correction. Technically the copy is made by the computer you are sharing it with, not the original.

My mind was dead-set on the printing press analogy for some reason.

Both are making copies, probably multiple, mostly transitory, along with any number of intermediaries.