Linux

One thing to note with X11's design, having a server and client, there was nothing requiring both to be on the same machine. You could run an X11 client on your local machine, ssh into a remote machine and use its X11 server.

Lets say you are home and can ssh into a work server. You could run Firefox on the work machine, using it's network and have the visual parts show up on your home computer.

This was very much a Unix, shared resource style design. Servers and thin clients. Put all your horse power in the big machine and connect using your crappy low power system to it.

For your second question, a window manager is the specific system that controls the placement of windows on an X11 desktop.

On a X11 based system, X11 is the windowing system (interacting with the video card) and a window manager is a system sitting on top of that laying out the windows and interacting with the user and other programmes. It is a separate programme on top of the X11 system, and communicates with X11, and X11 is the programme that communicates with the graphics card.

On Wayland, instead of 2 separate systems there can be 1 combined windowing systen that is both the window manager but also directly communicates with the hardware in a standardised way using the Wayland protocols. This is called a Wayland compositor.

Meanwhile a desktop environment is the whole desktop - that includes a window manager or compositor but also lots of other tools and software that together make a full desktop experience.

An example is KDE - KDE is a full desktop environment. It uses its own x11 window manger called kwin (and also able to be a wayland compositor), but it also uses a whole range of other tools alongside that to give you panels, widgets, desktop icons, a clock, menus, settings etc collectively forming Plasma desktop. And then on top of Plasma there is a whole range of bespoke programmes that form the full deskop experience - like Dolphin (file manager), Kate (text editor) and so on. All that software is designed to work seamlessly with the KDE family of tools and systems. The window manager, the desktop tools and the other programmes together form the whole desktop environment. But other desktop environments software will also work - for example Gnome based software can also run with KDE without issue and vice versa.

Gnome has its own window manager/compositor, and it's own widgets and tools to make a desktop, and it's own bespoke software to make a whole desktop environment.

And there are many others.

So in summary:

• Window Manager - the specific system that controls the placment and look of the individual windows talking to X11 which then talks to the hardware

• Wayland Compositor - the system that controls the placement and look of windows, using wayland protocols to speak to the hardware

• Desktop Environment - the whole desktop including the Window manager but also lots of other programmes and tools that form the basic desktop (such as a panel, menus, desktop icons) and the whole environment (other software like a file manager, text editor, calculator etc). KDE and Gnome are examples of popular desktop environments

Humorously, X11 is like driving a 1990 Honda Accord. It was built ages ago, but with enough care, it still runs just fine.

The good news? Over time, you’ve bolted on all sorts of modern conveniences: GPS, Bluetooth, maybe even a backup camera—but at the end of the day, it’s all just stuff you crammed in. Underneath, it’s still the same old car. It’s reliable, it gets great gas mileage despite the half a million miles on the odometer, and it’ll start even when it’s buried under a foot of snow. Sure, it takes some effort to pass emissions, but at least every mechanic knows how to fix it, and parts are cheap.

Now for the bad news. Anyone with a flathead screwdriver can take it for a joyride whenever they feel like it. You keep finding it parked in weird places, but hey, at least they always bring it back. The airbags? They might work, but there’s only one way to find out. And let’s be honest—most modern cars have surpassed it in every possible way.

The best part? It’s been paid off for decades. No one is just going to hand you a brand-new car because that would take a ton of money and effort. No matter how much you tinker with it, it’s still a 1990 Honda Accord. You can throw on some new tires, upgrade the suspension, and maybe swap out the brakes, but at the end of the day, it’s never going to have that brand new car feel.

• X11 is the displayer server, a real process running on your computer.
• X11 window managers are clients to that server. It communicates with the server and tells it where to draw the windows.
• A desktop environment is a window manager plus a whole suite of other applications and processes that a common computer user would expect.

A window manager and display server are the bare minimum of the x11 graphical environment. Desktop environment is draw the rest of the owl.

Wayland is is a completely different beast than x11. There is no Wayland program, just a wide set of protocols. There are no Wayland window managers, just "compositors". Compositors are responsible for everything both the display server and window manager would do in x11. Everything is up to the compositor to implement. It just has to follow the Wayland protocols.

This can make migrating to Wayland a bit tricky. If a program worked in one x11 window manager, it was basically guaranteed to work in all window managers becuase it was always communicating to the same X server directly. In Wayland that's not guaranteed. If a compositor didn't (or didn't correctly) implement a certain subset of protocols then the utility wouldn't work correctly.

IE take xrandr and wlr-randr. They both are a , "display settings" CLI utility. xrandr works on any x11 environment because it always communicates with x11. wlr-randr only works if the compositor implements the wlr_output_management_unstable_v1 protocol. See the protocol deifnition here

You can’t use xscreensaver on wayland.

In short, X11 is a bit unsecure in its concept (like every program can read keyboard inputs you are doing right now). The multi monitor configuration possibilities and mixing different setups is basically impossible (I mean stuff like mixing 4k@120 Hz with G-Sync and another one with 1080p@60 Hz with just V-Sync). X11 or XOrg has a long history since the 80s with many versions, the code base is spaghetti code and its not a pleasure for developers to work on.

Wayland is new, with a fresh and modern code base. It eliminates the security and monitor issues. Programs not written for Wayland does not work, but luckily there is XWayland, which allows running X11 games on Wayland. You can think of like Proton for X11, but without the benefits of Wayland, just a compatibility mode. In Wayland there are sub protocols, meaning standard definitions, that are developed and added after some time passes. I personally think protocols being like an addon that allows doing more stuff in a standardized way across all systems that support it. Developers in Wayland have a much better time working with its modern code base.

Have a look at https://wayland.freedesktop.org/docs/html/ch03.html .

the shortest simplest explanation is that X11 was designed around the idea that multiple user terminals would connect to one large mainframe computer, not everyone just having their own machine like actually became commonplace.

Before Wayland, there was X Window System, created in 1984. X Window System was designed in a time where you had one good computer connected to multiple displays used by different people. X went through many versions but version 11 (X11) stayed around for a long time.

But the architecture just isn't good. It wasn't designed for modern needs. MacOS used to use X, but replaced it to fit modern needs. Windows didn't use X, but they too updated Windows to fit modern needs. But Linux and other OSs stuck with X for a lot longer, hacking it to make it work. Honestly, it's amazing how well it does work.

But isn't not great. It wasn't designed with security in mind, it doesn't do multi-monitor well. Behind the scenes, it considers everything to be one giant display; issues arise when it comes to mixed-dpi displays and when monitor refresh rates don't match. It's also just a bloated, old code base that people don't want to work on. Fixing X would not only be difficult, but would break compatibility.

So people got working on a modern replacement for X aiming to avoid its issues. Wayland is leaner, more opinionated, and designed for how modern hardware operates. Wayland itself is just a protocol (like X11), and there's many different implementations of that protocol: Mutter, Kwin, wlroots, smithay, Mir, Weston, etc. Meanwhile X11 pretty much only had one relevant implementation, Xorg. Wayland's diversity has its pros and cons. Pros include (1) you can create your implementation in any programming language you want rather than being stuck to just one, (2) an implementation can fill just the needs on the person making it rather than trying to generalize it for everyone. But cons include the fact that this fragmentation leads to scenarios where one implementation supports something that others don't and implementation-specific bugs.

Wayland's opinionated design is also draws criticisms. It gives a lot of control to the compositors rather than windows, which is how Xorg, MacOS, and Windows work. Nvidia's wayland adoption was also slow and terrible. It took many years to get it into the only decent shape it's in now.