The Desktop Window Manager is Windows Vista and Windows 7‘s window manager that allows you to use Windows Aero and its subsequent theme. Some versions of Windows have it omitted; these are Vista Starter Edition and the Vista Home Basic has a cut down version of it, lacking the transparent glass and Flip 3D. It requires the user to have a video card capable of running Direct X 9.0 and Shader Model 2.0. So, what does it do? Well, it gives you nice effects, such as the program thumbnails when you hover over them in the taskbar, the 3D Alt-Tab (if you don’t know what I’m talking about and you’re on a Windows Vista or Windows 7 machine, use Win+Tab – you’ll be impressed).
Now, onto the more technical side of it – the desktop window manager is a compositing window manager. This means that each program will write data to its individual buffer. Then the Desktop Window Manager composites the program buffer into an image. This varies from earlier versions of Windows where all programs would write to the same, shared buffer.
It goes under the name ‘dwm.exe’ and if you are running Windows Vista or Windows 7, you’ll see it in your task manager. It tends to use 30-50MB of memory, and that will increase if you have a lot of windows open (obviously, as more program buffers which all require memory). If you’re running out of memory and want to reduce this then just switch to the Vista Basic Theme. It won’t eliminate in entirely, but it will use much less memory (typically in the region of 2-3MB). If you truly want to get rid of it (not recommended by the way) then open services in Control Panel, find ‘Desktop Window Manager Session Manager’ and simply press the stop service button. Once you do this you will be switched to the Vista Basic Theme. If you want dwm.exe to be disabled permanently then double click on ‘Desktop Window Manager Session Manager’ and change Start Up type to disabled.
You might have noticed it was called ‘Desktop Window Manager Session Manager’. What does session manger mean? Well it means that it keeps track of your open applications and what files have been accessed by the open applications. This is so when you put your computer in sleep mode, it can remember what needs to be open and running when you wake the computer up again. Windows doesn’t have such a thing built into the core of the operating system, so Desktop Window Manager helps keep track of it instead.
In conclusion, the Desktop Window Manager (dwm.exe) is a Windows Vista and Windows 7 program/service that allows you to use all those fancy effects. Don’t disable it unless you know what you’re doing – I’d recommend just switching to the Basic Theme if you’re that concerned about memory usage. It also works as a session manager. In summary, a very useful service that very few people know about, but most use it on a daily basis.