> (Likely also a bad experience with modern Linux on 30gb.)
I just did an install of modern Linux (the latest CentOS 7, with Gnome deskop), so I can check. The root partition is using at the moment 4.2G, plus a 2.0G swap partition and a 1.0G boot partition. So if this were a 30G disk, I'd have more than 20G left, even after installing a few applications.
There's plenty of serious Linux distros that still ship on a single CD. Arch Linux, for example, comes on a 522 MB ISO. That gets you a basic functional desktop environment, and anything else you might need can be installed from the Net.
There is no desktop on the 522 MB Arch Linux ISO, or if there is, I've never seen it. It boots into a root shell on tty1, and is only supposed to be used for installation. I would be very surprised to even find an X server in there.
EDIT: For a more realistic number, I just checked my Arch-Linux-based home server, which has a fairly small installation (including some multimedia and X11 stuff for PulseAudio, mpd and youtube-dl, though). Needs just over 2 GiB for the entire system and applications:
df / -h
Filesystem Size Used Avail Use% Mounted on
/dev/sdc2 110G 2,2G 103G 3% /
Of course, you should have some breathing room, but usually not more than 8 GiB on a server, and maybe 16 GiB on a desktop.
So consumer-oriented distros don't seem to be nearly so much lighter than Windows. With the caveat that Ubuntu probably comes preloaded with more apps like Libre Office.
I just installed Ubuntu 16.04 a month ago (new laptop), and with /home/ on its own partition, after installing everything I use regularly, root is only using 9.3G
A decent amount of that space ends up being on-disk swap for the RAM, for what it's worth. And note that, on that same page, Xubuntu and Lubuntu are offered up as alternatives for less performant computers. They only require 5 GB of space. Windows doesn't have a light version like that.
I just did an install of modern Linux (the latest CentOS 7, with Gnome deskop), so I can check. The root partition is using at the moment 4.2G, plus a 2.0G swap partition and a 1.0G boot partition. So if this were a 30G disk, I'd have more than 20G left, even after installing a few applications.