what's the term for double window in one window frame and why is it considered outdated technology?

I live in Montreal and I just moved from a building that had double sliding windows in each window frame (I assume a single pane each) to a building with single double-pane windows that look a lot newer. The heating bill for the new apartment is much larger and the soundproofing is non-existent, I have a volume of street noise that sounds like my windows are open at all times, I can hear two people talking on the other side of the street (I am on the second floor).

As per my limited experience, the double window technology (two single panes) seem to be a lot better than the newer windows in the new apartment. That's what my parents in Russia seem to have too and the second window was installed on the interior for the winter only and removed during summer.

I would like to do some research online, but I am not sure what to even call the double window set-up, nothing comes up. Any tips? What's your experience with this?

Edit: Interior Storm Windows seem to be the best term so far. The question remains - why is this considered an outdated technology? Again, from my limited experience it seems better to me in every way than any fancy new windows.