A Windows Manager, shortened to WM, is a type of software used on a wide variety of operating systems that defines the overlay mode, size, position and appearance of windows on the screen, minimizing or maximizing them, allowing the user to manipulate the windows and launch new applications.
A window manager may be part of the graphical interface of a desktop environment or may exist autonomously.
Window managers are different in appearance, RAM consumption, customization options, similar to existing desktop environments, and so on.
All graphical desktop operating systems have a window manager system.
Both Microsoft Windows and Apple Mac OS X contain a standard window manager integrated within the operating system.
The X Window graphical system, used for GNU/Linux systems, allows the user to choose between several window managers.
The window manager can be simplified (twm, evilwm), or provide the functionality of a complete desktop environment such as Enlightenment, Fluxbox, fvwm.
Window managers can be divided into four categories depending on how they manage the windows.
1. Window managers that allow windows to be created or compounded separately and then combined and displayed.
2. Window managers who use overlapped or stacked windows.
3. Window managers that position the windows as frames so that they occupy the entire screen without overlapping.
4. Window managers that allow windows to be changed between the two overlapping modes or frame.
The first category allows a wide variety of interface styles and the presence of 2D and 3D visual effects. Mac OS X was the first operating system with a windows composer manager followed by the Linux family of distributions and later Windows. The most commonly used composite window managers are Compiz, Kwin, Xfwm, Enlightenment, Mutter, Desktop Window Manager, Quartz Compositor.
The second window manager allows multiple windows to be placed on the screen as superimposed sheets of paper, such as Amiwm, Blackbox, Fluxbox, FVWM, IceWM, Openbox, Window Maker.
In the third category of windows manager, the keypad is used to control the windows, with poor mouse support, for example, awesome, dwm, ion, larswm, ratpoison, stumpwm, wmii, xmonad.
In the fourth category we have awesome, bluetile, dwm, echinus, FVWM, i3, larswm, spectrwm, xmonad.
As I said, the X Window graphical system, available in GNU/Linux systems, allows the user to choose between several window managers.
The most popular Linux Windows Manager are:
AfterStep, based on FVWM
AmiWM (Amiga Window Manager)
BlackBox
Compiz, 3D interface
Enlightement
Fluxbox
FVWM
Icewm, compatible with Gnome and KDE
Kwin
Marco, comes as a standard for MATE
Metacity, window manager for some versions of GNOME 2
Metisse, Compiz alternative
Motif Window Manager (MWM)
Muffin, default for Cinnamon
Mutter
Openbox, originally based on Blackbox, for LXDE
Sawfish
WindowMaker
Xfwm in Xfce
While in Microsoft Windows the WM used is Desktop Window Manager (DWM) while in Mac OS X it is called Quartz Compositor.
The amount of memory usage that the dwm.exe process requires depends on the number of open windows because each window requires a specific place and a quantity in memory to store the contents of that particular window. Consequently, the more open windows you have, the more memory will be used by dwm.exe. The advantage of using a composite window manager is that in most cases a relatively small amount of memory is actually used.