Microsoft OS/2 Version 1.x Entries in the Registry

The Microsoft OS/2 version 1.x subsystem starts whenever a user starts an OS/2 character-based application on an x86-based computer. The Registry entries for the OS/2 subsystem are found under this key:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet
    \Control\Session Manager\SubSystems

The Os2 entry in this subkey describes the path to the executable file used to start the OS/2 subsystem. The directory path for the OS/2 library is the Os2LibPath value defined under the Session Manager\Environment subkey.

When Windows NT is installed on a computer, if Setup finds a copy of CONFIG.SYS for OS/2, a copy is placed in the SystemRoot\SYSTEM32 directory. This information is used to configure the OS/2 subsystem whenever an OS/2 application is started. If a CONFIG.SYS file is not found, a substitute is created in the Registry, with the following values:

PROTSHELL=C:\os2\pmshell.exe c:\os2\os2.ini c:\os2\os2sys.ini
    %SystemRoot%\system32\cmd.exe
SET COMSPEC=%SystemRoot%\system32\cmd.exe

The OS/2 CONFIG.SYS information is stored in the following Registry entry, which appears only after an OS/2 application has been run on the system:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\OS/2 Subsystem for NT\config.sys

The other subkeys under the OS/2 Subsystem key do not contain entries.

If you subsequently edit the C:\CONFIG.SYS file using a text editor, LIBPTH=, SET PATH=, and Set WINDIR= entries are appended to the end of the file from the Windows NT environment. Any changes made to the path or environment variables take effect after the system is shut down and restarted.

For details about managing this environment under Windows NT, see Chapter 11, "Other Application Environments," in the Windows NT System Guide.

You can disable an OS/2 subsystem in Windows NT and still run a bound application under a VDM. Many bound applications run better under a VDM than under the OS/2 subsystem.

To disable the OS/2 subsystem in Windows NT

• In Registry Editor, change the value of GlobalFlag to 20100000 in the following Registry path:

  HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\SessionManager

You can also use FORCEDOS.EXE, a utility supplied with Windows NT in the SystemRoot\SYSTEM32 subdirectory. This allows you to run a bound application under a VDM. To see how to use the ForceDOS utility, type forcedos /? at the command prompt.