By default, the UDMA66 mode is disabled on a computer that is running Microsoft Windows when the computer uses a Intel chipset that supports UDMA66. This behavior is by design.

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Enable the UDMA66 mode

Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:

•	Make sure that the device supports UDMA66 mode.
•	Use an 80-pin IDE cable with the correct pin cut.
•	Add the following registry key: 1. Start Registry Editor. 2. Locate the following key in the registry: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Class\{4D36E96A-E325-11CE-BFC1-08002BE10318}\0000 3. On the Edit menu, click Add Value, and then add the following registry value: Value Name: EnableUDMA66 Data Type: REG_DWORD Value: 1 4. Quit Registry Editor. 5. Restart the computer.

Note For more information about the IDE cable, contact the hardware manufacturer.

When you restart your computer, the UDMA66 mode will be enabled if the mode is supported by the hardware.

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