Just the kernel or the distributions?

2.2 introduced usb support.

Configuring XFree86 was the first thing I thought of. Also recompiling the kernel was a common thing to do. A lack of any DE (just a bare WM, so no fancy clipboard or anything).

I remember using the 2.6.x kernels, how it was a hassle to set up X, and to rebuild packages for certain GPUs. Heck, I faintly remember using Xfree86 and changing the configuration files.

if this is just the kernel, i guess amd drivers?
if this includes distributions: gnome isn't dogshit anymore, wayland, systemd everywhere, abundance of graphical "app stores", more filesystems to choose from, much easier to setup wine through lutris/pol

no iptables pre 2.4, handling of /dev, no /sys

what i learned (from the academic side.. mind you)
was the scheduler was changed dramatically in these versions
from a practically round robin scheduler in 1.x eventually culminating in cfs

I'd like to see @joeyh and @EtchedPixels chime in. Maybe @kragen as well.

Looking at systems as a whole:

- There was the pre-distro stage.

- First distros, notably SLS and Yggdrasil. I've heard SLS ("Soft-Landing Software") was called that "because it was a pile of shit". It worked, but barely.

- The packaging formats. Slackware, Red Hat, and Debian, each organised around a specific packaging format and philosophy, emerged at nearly the same time, about 1994.

- XFree86. Having an X11 impleentation made a huge difference and impact.

1/

Graphical installers; you don't need to do much at all these days during install.
Rare to need to hand configure X, as opposed to the first 10 years+ of editing X conf.
Hotplug everything - so hand configuring mice/keyboard/displays makes little sense.
Hotplug storage just working.
Fonts and languages just working - unicode+fonts meaning everything renders.
NetworkManager - wifi/vpn etc just works.
Modern Initramfs's larger than the hard disks I used to install whole systems on 😞

@codesections Having been around since Linux 1.2-ish, I found this intriguing to ponder. And actually, the only massive singular change I can recall is the move from a.out to ELF binary format. Maybe the iptables introduction and farewell could count, too. Everything else went really gradually... at least that's how I remember it. Userland had much more step changes.

I'm spacing the revisions where they appeared, but the introduction of /proc was a pretty big deal, as was having a dynamic /dev. I would also argue that namespacing as a first-class citizen would be another major change, but some little bits of that go way back to pre-1.X for chroot, so that one is a bit trickier to cleanly define.