Hot Docking Support in Windows 2000 (257544)

MORE INFORMATION

Hot docking or undocking means docking your portable computer with or undocking your portable computer from a docking station while the computer is fully powered. The only way to know whether your system fully supports hot docking, from a hardware perspective, is to check the computer manufacturer's documentation or contact the manufacturer's Technical Support staff. For hot docking to work in Windows 2000, the following requirements must be met:

• The hardware must support the ability to hot dock and undock electrically.
• The computer must have an Advanced Configuration and Power Interface (ACPI) BIOS. (Microsoft Windows 95/Microsoft Windows 98 supports hot docking on computers with an Advanced Power Management [APM] BIOS; Windows 2000 does not.)
• The ACPI BIOS must be fully ACPI compliant and must meet the Windows 2000 standards for hot docking. (Many computers that were available at the release of Windows 2000 may require BIOS updates to work properly with Windows 2000.)
• Windows 2000 must be notified before an undock event occurs (and when hardware is removed from the system).
  
  Windows 95/Windows 98 performs a full enumeration upon each resume from suspend to support APM and ACPI. Therefore, Windows 95/Windows 98 does not require notification when hardware is removed. Windows 2000, which supports only ACPI BIOS implementations of hot docking, follows the strict ACPI rules that state that the operating system must always be notified of hardware removal. Because notification is required by Windows 2000, there is no need for an enumeration upon resuming. This results in faster resume times.

Supported vs. Unsupported

In this article, "supported" means that hot docking and undocking should work and that Microsoft Product Support Services will provide reasonable-effort assistance in making hot docking and undocking work. "Unsupported" means that hot docking and undocking may work, but most likely will not, and is not recommended with Windows 2000. Windows 2000 will also display a message if you do something that is unsupported, such as performing a "surprise" undock (assuming that the system is still running correctly).

Supported Docking and Undocking Methods

• Hot docking and undocking: The computer is fully on. This is supported if the hardware supports it and if you always notify the system before removing the portable computer. Ways of notifying the system include using an external "Undock" switch or by clicking Eject PC on the Start menu. This is the same as Windows 95/Windows 98, except that Windows 2000 requires a fully compliant ACPI BIOS. Note that you cannot remove the portable computer from the dock manually without notifying the system in any Microsoft operating system.
  
  Note that some systems do not physically block you from trying to do this.
• Cold docking and undocking: The computer is fully off. This method is supported.

Unsupported Docking and Undocking Methods

• Warm docking and undocking: Undocking while the system is suspended or hibernating, and then resuming once undocked. This is unsupported. Avoid warm docking and undocking at all costs. In effect, this is the same as adding devices while the system is hibernating or on standby; in both cases this causes at minimum a surprise remove event (if the system is able to resume at all).
• Surprise undocking: A typical "surprise undock" scenario involves a manually ejectable system on which you suspend or hibernate the computer while it is docked, and then remove the computer manually and resume it. This is unsupported. Ejecting a computer that supports an undock switch while it is hibernating results in a surprise undock because the BIOS does not notify the operating system. In this case, Windows 2000 does not know that the hardware is gone (has been removed) and may attempt to access that hardware.

Notes

• Hot docking is disabled when legacy (non-Plug and Play) drivers are present. Any legacy driver causes the undock (and standby) option to be unavailable. This occurs because legacy drivers do not support power management and do not allow the system to stand by or hibernate.
• Hot-docking is not recommended when ISA Plug and Play adapters are present in the docking station. There is no way for Windows 2000 to differentiate between ISA Plug and Play devices in the laptop computer and those in the docking station. Windows 2000 may not be able to tell which devices to remove upon undocking.NOTE: Changing the display resolution whilst docked and connected to an external monitor followed by undocking will cause the previous display resolution to be selected for the on-board display panel.

For additional information about power management in general, click the article numbers below to view the articles in the Microsoft Knowledge Base: