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Maintaining Desktop Health : Understanding the Windows System Assessment Tool

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4/17/2013 4:02:57 PM

You can use the Windows System Assessment Tool (WinSAT) to assess the features, capabilities, and attributes of a Windows Vista PC. WinSAT executes during out-of-box-experience (OOBE) and when the Rate This Computer option is selected in the Performance Information And Tools control panel. This section discusses the Performance Information And Tools control panel in more detail. This section also describes how Desktop Window Manager performs composition and how Windows Vista determines which level of Aero Glass can be supported given the system’s hardware configuration.

Overview of WinSAT

Each assessment name has a set of assessment parameters that it will accept. For brevity, the assessment parameters are not provided here. To see the available assessment parameters, type winsat /? from an elevated command prompt.

Assessment Names

WinSAT assessment names include:

  • dwm The Desktop Window Manager (DWM) assessment is targeted at assessing a system’s ability to run a Windows Vista–composited desktop, often referred to as Aero-Express, Aero-Glass, or Aero-Diamond. Note that these are names of Aero themes. You can only run this assessment on computers with WDDM video drivers.

  • d3d The Direct3D (D3D) assessment is targeted at assessing a system’s ability to run games.

  • mem Runs system memory bandwidth tests. This is intended to be reflective of large memory-to-memory buffer copies, like those used in multimedia processing (video, graphics, imaging, and so on).

  • disk Measures the performance of disk drives.

  • cpu Measures the computation ability of the processor.

  • media Measures the performance of video encoding and decoding.

  • features Enumerates relevant system information. This assessment is automatically run once for each invocation of WinSAT and the data saved in the XML output.

  • formal Runs the full set of assessments and saves the result.

  • mfmedia Runs the Media Foundation based assessment.

Examining the Features Assessment

WinSAT automatically runs the Features assessment each time it runs. This assessment enumerates system information relevant to the assessments, including:

  • The name of the computer. Note that this information is supported only in private builds of WinSAT and will not be present in the retail version of the product.

  • An optional globally unique identifier (GUID) if the -igCid command-line switch is used. This ensures that each XML file has a unique identifier.

  • The iteration value from the -iter <n> command-line switch.

  • The number of processors, cores, and CPUs.

  • The presence of CPU threading technology.

  • x64 capability.

  • The processor signature.

  • The size and other characteristics of the processor’s L1 and L2 caches.

  • The presence of MMX, SSE, and SSE2 instructions.

  • Information on the memory subsystem. (Note that this is very system-dependent: Some systems will produce good detail here, others will not.)

  • Graphics memory.

  • Graphics resolution.

  • Graphics refresh rate.

  • Graphics names and device IDs.

Direct from the Source: WinSAT Data Files

Advanced users may want more information regarding the Windows Experience Index and system performance than is present in the Performance Information and Tools Control Panel. The underlying technology that supports the Windows Experience Index is the Windows System Assessment Tool (WinSAT). This tool stores the 10 most recent assessments in a data store folder located at:


The data store consists of XML files that contain information regarding each assessment. These XML files contain advanced details regarding system performance and the Windows Experience Index. The files are named by the date and time the assessments ran.

Quais Taraki, Program Manager

Windows Performance

Command Line Usage

Although in most cases, WinSAT will not be executed manually from a command prompt, the general format of the command line is

winsat <assessment name> <assessment parameters>

The WinSAT command-line options are not case sensitive. The command line does not require a dash for forward slash for the assessment name, but does support either a leading dash (-) or a leading forward-slash (/) character to designate an assessment parameter. An error will be reported if any options or switches are not supported.

The WinSAT tool also supports several command-line switches in addition to the assessment parameters. These are parsed by WinSAT before it passes control to one or more of the assessments. Some of these parameters are also supported by one or more assessments. Parameters that are not handled by assessments are stripped from the command line before the command line is processed by the assessments.

The command-line parameters recognized by WinSAT are:

  • -help or -? Displays the help content.

  • –v This specifies that WinSAT should produce verbose output. This output includes progress and status information, and possibly error information. The default is for no verbose output. This switch is passed to all of the specified assessments.

  • -xml <file name> This specifies that the XML output from the assessment is to be saved in the specified file name. All assessments support the –xml command-line switch; a pre-existing file with the same name will be overwritten.

  • –idiskinfo Information on the disk subsystem (logical volumes and physical disks) is not normally saved as part of the <SystemConfig> section in the XML output.

  • –iguid Generates a globally unique identifier in the XML output file. Note that this is not valid with the formal assessment.

  • -iter <n> Includes the iteration number <n> in the XML output file.

  • –ssc This causes WinSAT to skip checking the XML output against the WinSAT XML schema. Note that this command-line switch will be deprecated in release candidate versions.

  • –csv This causes WinSAT to save the top-level measured metrics to a CSV file.

Binary Components

WinSAT contains the following files:

  • Winsat.exe The executable. This file is located in the %windir%\system32 folder.

  • WinSAT.wmv The recommended video clip for use with the media decode assessment. This file is located in the %windir%\Performance\Winsat folder.

  • WinSAT.prx The recommended encode configuration file to use with the media encode assessment. This file is located in the %windir%\Performance\Winsat folder.

Exit Values

WinSAT provides the following exit values:

  • 0 indicates all requested assessments were completed successfully.

  • 1 indicates one or more assessment did not complete because of an error.

  • 2 indicates one or more assessments did not complete because of interference.

  • 3 indicates that WinSAT was canceled by the user.

  • 4 indicates that the command given to WinSAT was invalid.

  • 5 indicates that WinSAT did not run with administrator privileges.

  • 6 indicates that another instance of WinSAT is running.

Registry Locations

WinSAT writes the assessment results to the following registry key:

HKLM\Software\Microsoft\Windows NT\CurrentVersion\WinSAT\

Value: VideoMemorySize – Size of the video memory, in bytes

Value: VideoMemoryBandwidth – Derived from compilation of video memory and display resolution

If these registry keys do not exist, WinSAT did not run during the installation or upgrade the operating system. To create these registry keys, run WinSAT from the command line or from Performance Information And Tools, discussed in the next section.

How Desktop Window Manager Performs Composition

The new Windows Vista desktop composition feature fundamentally changes the way Windows displays pixels on the screen. When you enable desktop composition, individual windows no longer draw directly to the screen or primary display device as they did in previous versions of Windows. Instead, their drawing is redirected to off-screen surfaces in video memory, which are then rendered into a desktop image and presented on the display.

Desktop composition is performed by a new component in Windows Vista, the Desktop Window Manager (DWM). Through desktop composition, DWM allows for visual effects on the desktop as well as various features, such as glass window frames, 3D window transition animations, Windows Flip and Windows Flip3D, and high-resolution support.

Desktop Window Manager Components

The Desktop Window Manager consists of two main components: the Desktop Window Manager Session Manager service and the Desktop Window Manager process. The following section discusses these components in detail.

Desktop Window Manager Session Manager Service

The Desktop Window Manager Session Manager service starts and manages one Desktop Window Manager process for each user session on the computer. The Desktop Window Manager process runs as %SystemRoot%\system32\dwm.exe. If the process is ever terminated unexpectedly, it is restarted by the Desktop Window Manager Session Manager service.

The Desktop Window Manager process loads two important modules:

  • Udwm.dll Microsoft Desktop Window Manager DLL

  • Milcore.dll Microsoft Media Integration Library (MIL) Core Library

Windows Presentation Foundation

The Microsoft Windows Presentation Foundation (formerly codenamed Avalon) provides the foundation for building applications and high-fidelity experiences in Windows Vista and Windows Server Code Name “Longhorn,” blending together application UI, documents, and media content. The functionality extends to support for Tablet and other forms of input, a more modern imaging and printing pipeline, accessibility and UI automation infrastructure, data-driven UI and visualization, and the integration points for weaving the application experience into the Windows shell. The WPF components pf.dll and pc.dll are also clients to milcore.dll, which is loaded by the DWM service.

All of the Windows Aero and Glass features of the desktop are implemented through the Desktop Window Manager Session Manager service. This service is also known as the User Experience Session Manager Service (UxSms) and is implemented as a service that runs under the generic service host process svchost.exe.

WinSAT and the Desktop Windows Manager

WinSAT queries the system hardware and assesses the hardware capabilities of the computer. The Desktop Window Manager uses the data that WinSAT gathers to determine if the computer is capable of displaying the Aero Glass interface. WinSAT runs once during the out-of-box experience but can also be run manually by running WinSAT.exe from the command line or from the Performance Rating And Tools user interface.

Thresholds for Aero Glass Composition

Table 1 lists the VideoMemoryBandwidth threshold values, in MB/s, above which composition is enabled. If your value is above the threshold value required for Transparent Glass, you’ll get Transparent Glass. If your value is below the Aero Glass threshold value but above the Opaque Glass value, you’ll get Opaque Glass. Otherwise, you will not get glass composition.

Table 1. Thresholds for Aero Glass Composition
ResolutionThreshold for Transparent GlassThreshold for Opaque GlassRequired video memory for Transparent GlassRequired video memory for Opaque Glass
Single Monitor
800x600288,23458,45732 MB32 MB
1024x768388,84894,73532 MB32 MB
1280x1024526,766156,48164 MB32 MB
1600x1200687,589228,037128 MB64 MB
1920x1200814,702273,150128 MB64 MB
Dual Monitor
800x600376,21888,99832 MB32 MB
1024x768512,165144,52364 MB64 MB
1280x1024701,979239,123128 MB64 MB
1600x1200923,249348,809128 MB128 MB
1920x12001,094,897417,957256 MB128 MB

The values shown in the table are dependent on the resolution setting and availability of the Required Video Memory shown for each resolution setting to get composition.

These thresholds may be overridden, as explained in later in this section.

Troubleshooting Aero Glass

If your system is not displaying with Aero Glass, and you have met the minimum system requirements, you can use the following steps to diagnose the problem.

First, determine what display mode your system is currently in. The Windows Vista desktop has three distinct looks: transparent glass, opaque glass, and no composition.  Are you seeing opaque glass or are you simply not getting composition at all? A quick way to determine the level of composition is to look at the Minimize, Restore, and Close buttons on a window to see if they are docked at the top edge of the window:

  • Extended rectangular buttons indicate transparent or opaque glass.

  • Smaller square buttons indicate no composition.

Transparent glass is fully functional Windows Aero Glass. If you’re getting opaque glass, in all likelihood your computer has been assessed by WinSAT as not powerful enough to recommend transparent glass. The accuracy of the model by which this is evaluated will be increased in RC1 and RTM builds of Windows Vista, which may allow more computers to achieve an assessment that automatically enables transparent glass display.

WinSAT will write the following values to the registry during install if the computer is using a WDDM video driver. Computers with legacy video drivers will not generate these registry keys. These registry keys indicate what WinSAT detected for the video hardware.

HKLM\Software\Microsoft\Windows NT\CurrentVersion\WinSAT\
							HKLM\Software\Microsoft\Windows NT\CurrentVersion\WinSAT\

WinSAT generally assesses graphics subsystems correctly. However, in some cases the amount of textures and render targets WinSAT allocates causes the performance metric to be too low. This predominantly happens on cards with 64 MB or less of graphics memory.

If you’re not getting composition at all, the first step is to look at the Event Log to see what the problem is. Run Event Viewer, choose Windows Logs, and then choose the Application log. Look for entries with Desktop Window Manager as the Source. A recent entry should indicate why the Desktop Window Manager didn’t start. Possibilities include:

  • Not running a WDDM/LDDM driver.

  • Not running with 32 bits per pixel color. (To fix this, change your Display Settings and then log off and log on again.)

  • The monitor frequency is too low. (Realistically, this only happens with a faulty KVM, or if the computer was booted without a monitor.)

  • A mirroring device driver is in use.

  • An analysis of the hardware and configuration indicated it would perform poorly. In this case, the system may have been incorrectly assessed. If you believe it was, you can override this assessment, as explained in the next section.

Overriding Windows Vista Automatic Detection Mechanisms

On computers with WDDM-capable drivers, you can set the composition policy manually by setting two registry keys and then restarting the DWM. First, ensure that the following registry values are set:

  • Composition:


    Set to 1 (32-bit DWORD)

    The Composition key indicates whether composition is enabled or disabled. Setting this value to 1 will enable composition.

  • CompositionPolicy:


    Set to 2 (32-bit DWORD)

    The CompositionPolicy key determines whether you can use the WinSat assessment to enable or disable composition. Values are:




    Setting CompositionPolicy to 2 forces the system to ignore the WinSat assessment and enable composition.

Now restart the Desktop Window Manager Session Manager service by opening an elevated Command Prompt window with administrative privileges and typing net stop uxsms followed by net start uxsms at the command prompt.

Forcing WinSAT to Reassess the Computer

If WinSAT has not assessed the system at all or has incorrectly assessed the system hardware during install or upgrade, the Windows Aero Glass features will not be available. If you have installed new video hardware or other hardware that might affect the system rating, you may force WinSAT to reassess the computer.

To force WinSAT to run again and reassess the hardware, follow these steps:

Click Start, click Control Panel, and then click System And Maintenance.

Click Performance Information And Tools. From the Performance Rating And Tools control panel, click Rate This Computer or Update My Score. User Account Control will prompt you for permission to run the System Assessment Tool.

The rating dialog box will be displayed with a status bar. This process can take a few minutes. The screen may flash while the system is being assessed.

Examining Desktop Window Manager Performance

When the DWM process starts, it detects the video bandwidth and screen resolution to determine whether the computer can hit the target requirement of 30 frames per second, and then determines the state to start in: no composition, opaque glass, or transparent glass.

The desktop is normally rendered at 60 frames per second. If the DWM detects that it is taking longer than normal to render the desktop, a dialog displays, indicating a performance decrease has been detected. You will be prompted to take the one of the following actions:

  • Disable Desktop Composition Disable all desktop composition by the Desktop Window Manager service until the system is restarted or explicitly enabled.

  • Do Not Disable Desktop Composition, But Keep Monitoring Ignore the problem now and do not disable desktop composition. Inform the user again the next time a performance drop is detected.

  • Do Not Disable Desktop Composition, And Stop Monitoring Ignore the problem now and stop detecting performance reductions until the next system restart.

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