I went into the display adapter properties and 64 Hz rate is the only choice. Under 'List All Modes', the optimal is not available although there are many other choices that either do not work or are no better. My monitor and adapter drivers are up to date. System is HP Pavilion p6331p-b desktop, Windows 10, HP 2009m monitor. Microsoft has published a hotfix for the problem of the calibration curves unloading when the secure desktop launches in Vista. The fix is included in security.
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The Windows Display Driver Model (WDDM) is available starting with Windows Vista and is required starting with Windows 8. This section discusses requirements, specifications, and behavior for WDDM drivers.
NoteWindows 2000 Display Driver Model (XDDM) and VGA drivers will not compile on Windows 8 and later versions. If display hardware is attached to a Windows 8 computer without a driver that is certified to support WDDM 1.2 or later, the system defaults to running the Microsoft Basic Display Driver.
The following sections describe the Windows Display Driver Model (WDDM):
Note WDDM drivers do not directly use services of the Windows Graphics Device Interface (GDI) engine; therefore, the GDI section is not relevant to writing display drivers for the WDDM driver model.