The New Aero Glass : No More Warnings & Slowdowns!

Windows Vista introduced the Aero Glass user interface as a means to improve the look and feel of Windows while boosting productivity. However, DWM (Desktop Windows Manager) support for window transparency and translucency raised the memory requirements for PCs.

As we saw earlier, the amount of memory required to run multiple windows scaled linearly with the number of windows open on the system. The memory pressure was even higher on higher-resolution displays. In low-memory configuration systems, this left little system memory for other applications, thus affecting overall system performance by increasing the paging activity to disk. System responsiveness also decreased considerably as the paging activity increased.

Occasionally, the notification shown in Figure 1-3 appeared when a large number of windows were open and DWM consumed 25% of the total system memory.

When a user clicks on the notification, the following details appear.

After this warning appears, Windows Vista automatically turns off the Aero Glass theme if the system memory workload increases further to a point where DWM consumes 30% of the total system memory. Windows Vista then displays this message and flashes the screen to turn off the Aero Glass theme.

The system memory savings feature presents a great opportunity to enhance Windows performance on existing and newer hardware, eradicating the performance warnings and slowdowns shown above. Even though most low-end systems run the Aero Glass theme right out of the box, the performance of these systems under basic usage leaves some room for improvement.

One of the side-effects of using the Aero interface (DWM On) was the high memory consumption for each top-level window. On Windows Vista, GDI rendering required two memory allocations with the resolution equal to the size of each GDI window :

• A system memory allocation for GDI rendering
• A video memory allocation for DWM composition

For pure DirectX applications, Windows Vista required the following allocations :

• A video memory allocation for DirectX rendering
• A video memory allocation for DWM composition

For mixed-mode applications in which a window includes both GDI and DirectX content, Windows Vista required the following allocations:

• A system memory allocation for GDI rendering
• A video memory allocation for DirectX rendering
• A video memory allocation for DWM composition

With the smaller memory footprint in Windows 7, such performance warnings and slowdowns should no longer occur, even for low-end systems with limited system memory.

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