Windows 7 - True or False: Disabling Aero makes your computer slower.

A buddy of mine insists that disabling Aero (Desktop Window Management / DWM.EXE) will slow your system down (lets assume it has a mid level graphic card).

His logic is that Aero offloads some of the work to your GPU. Disabling it will increase CPU usage.

My logic is that DWM.EXE uses a "significant" amount of CPU, regardless of what the GPU is doing. DWM.EXE on most systems I've seen is usually at the top of the list when I go to task manager and sort by "CPU TIME". It uses more CPU time then my browser, more then explorer, etc etc.

So how can disabling it increase CPU usage? Where is this change reflected (which process shows increase CPU usage if you disable DWM)? How would you prove or disprove this?

Thoughts?

Desktop Windows Manager (DWM) Will uses CPU regardless because not all applications are made using the new features of DWM, in this case DirectX. A lot of applications are still using Graphics Device Interface (GDI) to draw their UIs. GDI in Windows Vista and 7 is mostly CPU bound. Now, the Aero window frames, all the UI effects and animations, all of the Aero feature set runs on the GPU. Turning off Aero or DWM you will not save anything concerning CPU usage or performance. Because all of the UI work will be pushed down to the CPU.

If all applications adopt the new way of drawing UIs then the CPU usage for DWM will lessen greatly.

I'd like to hear more about this, anyone got more info or good links? I maintain that my experience has been that disabling DWM causes less CPU usage (maybe me using multiple displays has something to do with it). On older systems it is even more pronounced.

If there is an increase in CPU usage when you disable DWM, where is it reflected on the task manager? Does each individual app use more CPU?

You just won't see the CPU usage like you do with DWM. Individual applications can use more CPU time but most of it will be used by System most likely. But no, you won't save anything. It just that DWM will use less CPU but that is because it goes else where.