The following values control startup parameters that affect MS-DOS–based applications and applications created for 16-bit Windows 3.1. The Registry path for these values is the following:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet
\Control\WOW
Cmdline REG_EXPAND_SZ Path and switches
Defines the command line that runs when an MS-DOS – based application runs under Windows NT. This command line continues to run until the related application is closed. The following switches can be included:
Switch | Meaning |
-a | Specifies a command to pass to the VDM |
-f | Specifies the directory to find NTVDM.EXE |
-m | Hides the VDM console window |
-w | Specifies the WOW VDM |
Default: %SystemRoot%\system32\ntvdm -f%SystemRoot%\system32 -a
LPT_timeout REG_SZ Number of seconds
Defines how many seconds after the LPT port has been used that Windows NT waits before grabbing the port, closing it, and flushing the output. This value should only be needed for MS-DOS -based applications that use BIOS and do not close the port.
Default: 15
Size REG_SZ Number in megabytes
Defines the amount of memory to be given to each individual MS-DOS VDM. The default of 0 gives the VDM as much memory as Windows NT determines is necessary, depending upon the memory configuration.
To change this value, change the related value in the PIF file for the application.
Default: 0
Wowcmdline REG_EXPAND_SZ Path and switches
Defines the command line that runs when a 16-bit Windows-based application is started. The switches instruct Windows NT to start either an MS-DOS VDM or a WOW VDM. See the definitions for allowable switches under Cmdline.
Default: %SystemRoot%\system32\ntvdm -m -w -f%SystemRoot%\system32
-a %SystemRoot%\system32\krnl386
Wowsize REG_SZ Up to 16 megabytes
For RISC-based computers, defines the amount of memory provided in a VDM when a WOW session is started. This value is not used on x86-based computers, where Windows NT allocates the memory needed when it is asked for.
The default size chosen for a RISC-based computer depends on the amount of system memory on the computer. For each MB specified, the system uses 1.25 MB, so setting Wowsize to 4 MB causes the VDM to allocate 5 MB, although applications can only use 4 MB. You can override the following defaults:
System memory size | Default VDM size |
Less than 12 MB (small) | 3 MB |
12–16 MB (medium) | 6 MB |
More than 16 MB (large) | 8 MB |
Caution Setting Wowsize to a value lower than 3 MB will cause most applications to fail.
Default: Depends on RISC-based computer's system memory