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What is the Windows Registry?

Where is the Registry?

How is the Registry edited?
Create a Shortcut to Regedit
Using Regedit to modify your Registry

The Registry structure

Backing up and restoring the Registry

Importing and Exporting Registry Settings

Cleaning out old data from the Registry

What is the Windows Registry?
The Windows Registry is a database used to store settings and options for the 32-bit versions of Microsoft Windows. It contains information and settings for  the PC hardware, software, users, and preferences. All system changes, like changing the screen saver, adding a sound card, and the installation and removal of 32-bit software, are stored in the Registry.

Where is the Registry?
The physical files that make up the Windows 95 & 98 Registries are stored in two hidden files in your Windows directory, called USER.DAT and SYSTEM.DAT. More information on the user.dat and system.dat can be found on our Resetting the Registry page.

How is the Registry edited?
The Registry Editor (REGEDIT.EXE) is included with Windows, but you won't find it on the Start Menu. Regedit enables you to view, search and edit the data within the Registry. While there are several methods for starting the Registry Editor, the simplest is to click Start, Run, and type regedit. You should see something like the image below.

Create a Shortcut to Regedit
to create a shortcut to the Registry editor,  right-click on a blank area of your desktop, selecting New, Shortcut. In the Command line box type regedit.exe and click Next, enter a friendly name (e.g. 'Registry Editor') then click Finish.

Use Regedit to modify your Registry
Once you have started the Regedit, you will notice that the left side is a tree with folders and the right is the contents (values) of the currently selected folder.

To expand a certain branch (see the structure of the Registry below), either click on the plus sign [+] to the left of any folder or double-click on the folder. To display the contents of a key (folder), just click the desired key, and look at the values listed on the right side. You can add a new key or value by clicking Edit, New or by right-clicking your mouse, and you can rename any value and almost any key with the same method used to rename files; right-click on an object and click rename, click on it twice (slowly), or press F2 on the keyboard. You can also delete a key or value by clicking on it and pressing Del (the Delete key) on the keyboard, or by right-clicking on it and choosing Delete.

Note: it is always a good idea to backup your Registry (see below) before making any changes to it. It can be intimidating to a new user and there is always the possibility of changing or deleting a vitual setting, which can cause registry corruption and force a reinstall of the whole operating system. It's much better to be safe than sorry!

The Registry structure
The Registry has a hierarchal structure, like the directory structure on your hard disk, with Regedit being similar to Windows Explorer. Each main branch (denoted by a folder icon in the Registry Editor, see below) is called a Hive, and Hives contains Keys. Each key can contain other keys (sometimes referred to as sub-keys) as well as Values. The values contain the actual information stored in the Registry. There are three types of values; String, Binary, and DWORD - the use of these depends upon the context. There are six main branches, each containing a specific portion of the information stored in the Registry:

HKEY_CLASSES_ROOT : Links with the HKEY_LOCAL_MACHINE\SOFTWARE\Classes sub-key. It Contains file association types, OLE information and shortcut data. This key, along with the pointer to the \Classes sub-key,   provides backwards comaptibility with Windows 3.X for OLE and DDE support.

HKEY_CURRENT_USER : Points to the section of HKEY_USERS appropriate for the user currently logged into the PC.

HKEY_LOCAL_MACHINE : Contains computer-specific information about hardware, software, and other preferences for the local PC. This information is used for all users who log onto this computer.

HKEY_USERS : Contains individual preferences for each user of the computer. Each user is represented by a SID (Security Identifier) sub-key located under the main branch.

HKEY_CURRENT_CONFIG : Links to HKEY_LOCAL_MACHINE\Config for machine-specific information.

HKEY_DYN_DATA : Contains information that must be kept in RAM. Windows occasionally swaps information out to the hard drive, which updates system.dat or user.dat, but the information in HKEY_DYN_DATA stays in RAM.

Backing up and restoring the Registry
Windows 98 comes with a Registry Checker. This utility will scan your Registry and look for old, out-dated or corrupt Registry entries. Once the scan is done, Registry Checker will automatically backup your Registry. Registry Checker can be run from the command prompt by typing scanreg if you are unable to get to Windows.
Windows 95: Microsoft included a utility on the Windows 95 CD-ROM that lets you create backups of the Registry on your computer. The Microsoft Configuration Backup program, cfgback.exe, is not installed by default, but it can be found in the \Other\Misc\Cfgback directory on the Windows 95 CD-ROM. This utility lets you create up to nine different backup copies of the Registry. These backups will be stored in your {Windows} directory with the extension RBK. cfgback.exe won't back up the USER.DAT file if your system is set up for multiple users.
You can copy the RBK file onto a floppy diskafter you have backed up your Registry. However, to restore from a backup, the RBK file must reside in the \Windows directory. Windows 95 stores the backups in compressed form, which you can then restore only by using the CFGBACK.EXE utility.

Importing and Exporting Registry Settings
A useful feature of the Registry Editor is the ability to import and export Registry settings to a text file. this file, with the REG extension, can then be saved or shared with other people to easily modify local registry settings. To test this, start the Registry Editor and "drill" down until you get to some sub-keys. Click Registry, Export Registry File..., choose a filename, select the Selected branch button,  and save. The file should be saved in the My Documents folder by default, but you can save it wherever you want. To view the file after you've saved it, find the file, right-click on it, and choose Edit. this should open the file in Notepad, and you should see someting like the following:

REGEDIT4

[HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Class\NetTrans\0001\Ndi]
"DeviceID"="MSTCP"
"MaxInstance"="8"
"NdiInstaller"="mstcp.dll,TcpNdiProc"
"HelpText"="TCP/IP is the protocol you use to connect to the Internet and wide-area networks."
"InstallInf"=""                         

The layout is quite simple, REGEDIT4 indicated the file type, [HKEY_LOCAL_MACHINE\SYSTEM\...] indicated the key the values are from. Lines like "MaxInstance"="8" are the values themselves. The information after the "=" will vary depending on the type of value it is; String, Binary, or DWORD.
Using Notepad, you can edit this file to make the changes you want, then it can easily be distributed. To add the file to a machine's Registry, double-click on it or choose Import from the Registry menu.

Cleaning out old data from the Registry
As mentioned before, Windows 98 includes a utility called Registry Checker that will scan and backup Registry files. Refer back to the Backing up and Restoring the Registry section for details.
Microsoft provides a tool for Windows 95 that will scan the Registry and look for old files, The program, RegClean, analyzes the Windows Registry and finds keys that contain erroneous values. After recording those entries in the Undo.Reg file, it removes them from the Windows Registry. This utility is not included in the Windows 95 CD, but you can download this free utility from our downloads page.

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