16 bit processes

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The 32 bit version of Windows XP will usually only open one 16-bit process and put all 16-bit apps running on the system into that process. This is necessary for some older applications that run together and share resources. But most 16-bit applications work better when they have their own dedicated resources. With the following registry change, the process is put in a "Win16 VDM" (16 bit Virtual DOS Machine) which doesn't allow any interaction with other processes. This is also called a WOW (Windows On Windows) process.
  1. Navigate the registry to
    • HKLM
    • System
    • CurrentControlSet
    • WOW
  2. change the setting
    • type= REG_SZ
    • name= "DefaultSeparateVDM"
    • value=
      • Yes if you have plenty of RAM
      • no if you are short on RAM
This is only necessary on a win32 version of XP since 16-bit processes don't exist in the 64-bit version. references
  • Programming the VDMDBG and enumerating the 16 bit processes
    http://support.microsoft.com/kb/q182559/
  • the "DefaultSeparateVDM" setting
    http://www.microsoft.com/technet/prodtechnol/windows2000serv/reskit/regentry/29997.mspx?mfr=true
  • Sean Daily's article in WindowsITPRO
    http://www.windowsitpro.com/Windows/Articles/ArticleID/3022/pg/2/2.html