If you weren't handling data for more than one player, weren't processing the BGS at all, etc. the "offline" version of the game wouldn't be noticeably bigger on disk than the current online version.
ed milky way = 400 billions systems, each system has a 64 bit word address, so 3.2 Tera byte to store the galaxy, correct ?
Incorrect - it's
much more abstract than that. It would take that much to store the entire galaxy in a conventional database, but they don't - one of the most impressive Frontier achievements is that generation as needed from a tiny amount of "seed" data is fast enough to look like it's all there already.
Set your bandwidth monitor on and try doing a 20kLY route plot. The bandwidth use will be in the routine bytes/sec of "just playing the game" (assuming there's no other players about), the route will plot in a matter of seconds having passed through millions of stars worth of space, and you can even do things like apply a star-class filter to it to make it have to generate more than just "a system exists at this position" without really slowing it down.
No data transferred from servers, no gigabytes cached and retrieved from disk, and all with fairly low CPU and memory usage, too. Really impressive.
but there's probably TBs of DB storage happening right there.
Remember that Terabytes are
huge. If you're just storing text-style data, mostly numbers, the occasional string of words, even getting into gigabytes is tricky.
A complete EDDB data dump for inhabited space - and that's provided in a fairly inefficient uncompressed format for ease of use - takes less than a single gigabyte. Even accounting for various hidden variables and the markets for all the new Odyssey settlements EDDB doesn't know about yet, "non-player" data isn't going to be more than a couple of gigabytes total.
Once you add in players it gets a bit bigger - >12 million accounts potentially generate quite a bit of data, but they'd still be able to have 100kb each before the data got to a terabyte - a very active account probably has something like that or even more from exploration data, but the majority won't. Of course, for an offline version, you only need your own data and a couple of megabytes won't matter much. They
might be up to a terabyte or two by now, but I wouldn't be surprised if it was a lot less.