The Emergency Repair Disk (ERD)

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When a portion of the Windows NT Registry becomes corrupted, your workstation can become unstable and crash. In some instances, these errors even prevent you from starting your computer up and booting the Windows NT operating system itself. You can repair the Windows NT Registry by creating an ERD that contains the important system Registry information and using that disk to repair your system configuration.

An ERD contains backup information about your workstation’s security account manager (SAM) database, your system configuration, and important system configuration parameters. Also copied to the ERD are the two files required to create a virtual DOS machine (NTVDM): autoexec.nt and config.nt.

You are prompted to create an ERD when you install Windows NT Workstation. If you prefer, you can create an ERD at a later time. Regardless of whether you choose to create an ERD, the appropriate files are copied to the %systemroot%\Repair directory.

If you search for the topic of the Emergency Repair Disk in the online Help system, Windows NT Workstation’s Help system steps you through the process of either creating or updating your ERD. You can also open a Command Prompt window and create or update your ERD by using the rdisk.exe command.

RDISK performs the following functions:

• Copies the Registry default hive (HKEY_USERS\DEFAULT)
• Copies the Registry security hive (HKEY_LOCAL_MACHINE\Security)
• Copies the Registry software hive (HKEY_LOCAL_MACHINE\Software)
• Copies the Registry system hive (HKEY_LOCAL_MACHINE\System)
• Copies the workstation SAM
• Copies the Registry autoexec.nt file
• Copies the config.nt file

These files are copied into the %systemroot%\REPAIR folder. After these files are copied into the REPAIR folder, the RDISK utility prompts you for a floppy disk on which to create an ERD. The information in the REPAIR folder is copied on to this disk.




The ERD is only useful if you update it on a regular basis. You should consider updating the ERD before any major software installations or upgrades are performed, before any changes to your security policy occurs, and before the hardware configuration of your workstation changes. If this information is not current on your ERD, the restoration you can perform using the ERD is of limited value. The ERD doesn’t take the place of a full volume backup, it saves only data that can help re- establish your system configuration based on information contained in the Registry.

To create an ERD, follow these steps:

1.	Choose the Command Prompt command from the Programs submenu of the Start menu.
2.	Enter RDISK /S at the command prompt, and then press Enter.
3.	Click on the Create Repair Disk button in the Repair Disk Utility dialog box (see Figure 7.3).
4.	Insert a formatted floppy disk, and then click on the OK button.
5.	After Windows NT Workstation creates the ERD, remove the floppy disk, write-protect the disk, and store it away.
6.	Click on the Exit button to close RDISK.
7.	Click on Close.

The information copied to the ERD is in compressed format. To restore a Registry key by using the Registry Editor and the ERD data, expand the files by using the Windows NT Expand program. The following list of files are found on an ERD:

• autoexec.nt and config.nt. The two files responsible for a Virtual DOS Machine. They correspond to the autoexec.bat and config.sys files on MS-DOS. The first runs a batch file; the second sets an environment.
• default._. The compressed copy of the System’s default profile.
• ntuser.da_. The compressed copy of the ntuser.dat file, which stores user profiles.
• sam._. The compressed copy of the SAM hive of the Registry with a copy of the Windows NT accounts database. A workstation’s SAM doesn’t contain as much information as a server’s (especially a domain server) SAM does. Missing is information about other machine and user accounts that the workstation doesn’t know about.
• security._. The compressed copy of the Security hive with SAM and security policy information for your workstation’s users.
• setup.log. This text file has the names of the Windows setup and installation files, and checksums for each file. The file is used to determine whether essential system files are either missing or corrupt. If so, it replaces them in a recovery operation.
• software._. A compressed copy of the Software hive with information about installed programs and associated files and configuration information for those programs.
• system._. A compressed copy of the System hive of the Registry. This hive contains the Windows NT control set.

To update the ERD, run the RDISK program and select the Update Repair Info button and confirm that you want to overwrite the current repair information.

The importance of using the S switch for the RDISK program is worth noting. This switch updates the DEFAULT._ SECURITY, and SAM changes without requiring that you go through the Create Repair Disk? dialog box first. Without it, changes to your account information are not noted. If you have a lot of accounts, updating this information can take some time. Also, your ERD will likely expand beyond the single floppy disk limit. In that case, the RDISK program asks you for additional disks, as needed.