With Group Policy Objects in Windows, there is a "Hide these specified drives in My Computer" option that lets you hide specific drives. However, it may be necessary to hide only certain drive, but retain access to others.

There are seven default options for restricting access to drives. You can add other restrictions by modifying the System.adm file for the default domain policy or any custom Group Policy Object (GPO). The seven default selections are:

• Restrict A, B, C and D drives only
• Restrict A, B and C drives only
• Restrict A and B drives only
• Restrict all drives
• Restrict C drive only
• Restrict D drive only
• Do not restrict drives

Microsoft does not recommend to change the System.adm file, but instead to create a new .adm file and import this .adm into the GPO. The reason is that if you apply changes to the system.adm file, these changes might get overwritten if Microsoft releases a new version of the system.adm file in a Service Pack.

The whitepaper "Implementing Registry-Based Group Policy for Applications" explains how to write custom .ADM files. To view this whitepaper, please see the following Microsoft Web site:

The default location of the System.adm file for a default domain policy is: The contents of these folders are replicated throughout a domain by the File Replication service (FRS). Note that the Adm folder and its contents are not populated until the default domain policy is loaded for the first time.

To make changes to this policy for one of the seven default values:

1. Start the Microsoft Management Console. On the Console menu, click Add/Remove Snap-in.
2. Add the Group Policy snap-in for the default domain policy. To do this, click Browse when you are prompted to select a Group Policy Object (GPO). The default GPO is Local Computer. You can also add GPOs for other domain partitions (specifically, Organizational Units).
3. Open the following sections: User Configuration, Administrative Templates, Windows Components, and Windows Explorer.
4. Click Hide these specified drives in My Computer.
5. Click to select the Hide these specified drives in My Computer check box.
6. Click the appropriate option in the drop-down box.

These settings remove the icons representing the selected hard disks from My Computer, Windows Explorer, and My Network Places. Also, these drives do not appear in the Open dialog box of any programs.

This policy is designed to protect certain drives, including the floppy disk drive, from misuse. It can also be used to direct users to save their work to certain drives.

To use this policy, select a drive or combination of drives in the drop-down box. To display all drives (hide none), disable this policy or click the Do not restrict drives option.

This policy does not prevent users from using other programs to gain access to local and network drives or prevent them from viewing and changing drive characteristics by using the Disk Management snap-in.

The default values are not the only values that you can use. By editing the System.adm file, you can add your own custom values. This is the portion of the System.adm to be modified: The [strings] section represents substitutions of the actual values in the drop-down box.

This policy displays only specified drives on the client computer. The registry key that this policy affects uses a decimal number that corresponds to a 26-bit binary string, with each bit representing a drive letter: This configuration corresponds to 67108863 in decimal and hides all drives. If you want to hide drive C, make the third-lowest bit a 1, and then convert the binary string to decimal.

It is not necessary to create an option to show all drives, because clearing the check box deletes the "NoDrives" entry entirely, and all drives are automatically shown.

If you want to configure this policy to show a different combination of drives, create the appropriate binary string, convert to decimal, and add a new entry to the ITEMLIST section with a corresponding [strings] entry. For example, to hide drives L, M, N, and O, create the following string and convert to decimal. This binary string converts to 30720 in decimal. Add this line to the [strings] section in the System.adm file: Add this entry in the ITEMLIST section above and save the System.adm file. This creates an eighth entry in the drop-down box to hide drives L, M, N, and O only. Use this method to include more values in the drop-down box. The modified section of the System.adm file appears as follows: This [strings] section represents substitutions of the actual values in the drop-down box.

For additional information, click the following article number to view the article in the Microsoft Knowledge Base: