Windows NT Screen Acceleration

Screen acceleration is specific to the Windows NT platform. The Windows 95, Windows 98, and Win 3.1x Remote Control Agents intercept calls from the Graphics Device Interface (GDI) to the display driver, so there is no need for acceleration on these platforms. On Windows NT, the hardware abstraction layer (HAL) prevents this kind of interaction, which makes intercepting video changes on Windows NT computers somewhat more time consuming.

The Remote Control Agent on Windows NT 3.51 and Windows NT 4.0 both send raster lines between the client computer and the administrator’s computer (the server), but Windows NT 4.0 is much slower than Windows NT 3.51 because it must capture the entire screen continually to check for changes.

Windows NT video acceleration reduces the additional work associated with each screen refresh. Without Windows NT video acceleration, a full screen shot is taken of the entire desktop each time a DesktopChange event occurs. This bitmap is compressed and passed through the network to the viewing computer (the server). Windows NT video acceleration speeds the process by capturing a smaller rectangular region within which the user’s desktop has changed instead of capturing the entire screen. This reduces the size of each screen shot and increases the rate at which desktop changes can be passed across the network to the viewing computer.

The Windows NT 3.51 accelerator (Idis_nt.dll) notifies the Remote Control Agent where and when screen changes have occurred. The Windows NT 4.0 accelerator (Idisntkm.dll) intercepts calls to the Windows NT 4.0 display driver to indicate where and when screen changes have occurred.

To enable video acceleration, you must restart the computer at least once; multiple reboots might be required. (For more information about installing these video accelerators and using them with the resident video drivers, see “Details of Video Acceleration” later in this chapter.)

Whether video acceleration can be enabled depends on two items. First, Video Acceleration must be enabled on a site-wide basis by the site administrator. Second, the video driver name must be in the list of video drivers that can be accelerated. The list of video cards and drivers that can be accelerated resides on the SMS primary site server, in the Advanced tab of the Remote Control Configuration Properties dialog box. Although, theoretically, you can add to this list, the result of doing so is unknown. Deleting items from this list makes them unavailable for video acceleration, even if acceleration is enabled site-wide.

Procedure Bullet  To view the list of video cards and drivers that can be accelerated

  1. In the SMS Administrator console, navigate to:
    2. Systems Management Server   Lower levelSite Database (site code - site name)      Lower levelSite Hierarchy         Lower levelsite code - site name            Lower levelSite Settings               Lower levelClient Agents
  2. In the details pane, right-click Remote Control Client Configuration and then click Properties.
  3. Click the Advanced tab and then select Install accelerated transfer on Windows NT clients.
  4. Click Apply and then click OK.

This list is passed down to Windows NT clients, into the following registry key:

\HKEY_LOCAL_MACHINE\…\Sites\System\<Site_code>\Client Components\Remote Control

Video acceleration on Windows NT computers is accomplished with either the .sys file Idis_nt (for Windows NT 4.0) or the Idisntkm file (for Windows 3.51). The appropriate driver for the operating system is loaded into the appropriate System32 directory (System32\drivers for Windows NT 4.0). The driver is installed as an additional video driver to manage video acceleration during a Remote Control session. At no other time is the acceleration used on the Windows NT computer. Although the driver is loaded and running, it is only used during an accelerated Remote Control session.

The determination of whether a client’s video card can be accelerated happens at the time Remote Control is installed on the client.

Procedure Bullet  To determine whether acceleration is enabled on a particular client

  1. Using Regedt32 or Regedit, navigate to the following registry key:

    \HKEY_LOCAL_MACHINE\Hardware\Devicemap\Video.

  2. Review each of the Device\Video0 keys (there might be more than one) and take note of the Services\<video driver>\Device0 key on each.
  3. Use these keys as pointers to view the following registry key:

    \HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\<key value from the previous step>\Device0.

  4. Make sure that the InstalledDisplayDrivers key is set. It should list one or more display drivers.

Or, if the Remote Control icon is present on the client’s desktop, double-click it to open the status display window. The Remote Control status window will indicate whether acceleration is loaded in the appropriate status line.