Windows Registry

The Windows Registry is a unnecessarily nested key-value store.

Windows for Workgroups 3.11

The following things were noticed after installing the 16-bit version of Internet Explorer 5.01.

REGEDIT.EXE

This one is bundled with the operating system. Run it with the /v flag to make it actually usable.

• It only sees the type registrations (HKEY_CLASSES_ROOT in REGEDT16.EXE).
• In verbose mode, spaces in keys are replaced with #.
• There is only one value per key ((Default) in REGEDT16.EXE), and it is always a string.
• A "Revert to Last Save" menu item exists.
• Data is stored in %WINDIR%\REG.DAT.
• Separate REGEDIT.HLP and REGEDITV.HLP files exist. The latter is used for the Help menu when running in verbose mode.
• Verbose mode takes significantly longer to start than standard mode.

REGEDT16.EXE

This one comes with the 16-bit version of Internet Explorer 5.01.

• This gets dumped into %WINDIR%\SYSTEM unlike the native REGEDIT.EXE
• The About dialog states this is for both Windows 3.1 and Windows NT 3.51.
• HKEY_CURRENT_USER and HKEY_LOCAL_MACHINE are present too.
• String, Binary, and DWORD are the only types.
• Data is stored in %WINDIR%\REG16X2.DAT.
• REG16X2.Enn for 00-99 are created next to the file for each installation and uninstallation attempt.
• The program starts significantly more quickly than REGEDIT.EXE /V.

Native .REG file format

This section details the native format understood by Windows 3.1. 16-bit Internet Explorer 5.01 and the like instead use the newer REGEDIT4 format.

• The first line is REGEDIT with no version afterwards. Contrast this with REGEDIT4 and Windows Registry Editor Version 5.00 present in later versions.
• HKEY_CLASSES_ROOT is explicitly prepended to every key. Contrast this with REGEDIT.EXE /V strongly implying that the root is that itself.
• Every processed line has the format HKEY_CLASSES_ROOT\path\to\key = Value of key.
• Lines that do not start with HKEY_CLASSES_ROOT are ignored; no special character is needed to start a comment.
• If the  =  and value are omitted, the key is created without a value.
• Escape sequences are not understood.

KB articles

• Q78346: Windows: Maximum Valid Size for REG.DAT and .INI Files
• Q80393: How to Rebuild the Default Windows REG.DAT File
• Q81530: Cannot Use How To Use Help in Registration Editor
• Q82144: REG.DAT May Need Update if Both Windows 3.0, 3.1 Installed
• Q82650: OLE: SETUP.REG Can Be Used to Repair REG.DAT
• Q82810: Where Windows Searches for REG.DAT
• Q82814: Re-Registering .REG Files
• Q82821: Registration Info Editor (REGEDIT) Command-Line Switches
• Q84791: Associating Files and Passing Command-Line Parameters
• Q85326: Windows Err Msg: Failed to Register Server