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22.19 How to Set Up a Dual DOS/Windows Installation

Q: I want to be able to run DJGPP both under Windows 9X with long file names, and when I boot into plain DOS, where long file names aren't supported. How can I set that up?

A: Such a setup is possible, but it involves a few special actions, and some vigilance on your part during routine operations.

First, you must set the option in the Windows registry which prevents it from using numeric tails when it invents short 8+3 aliases for long file names. When numeric tails are enabled, and a file with a long name is created, Windows generates a short 8+3 alias for that long name by attaching to the first 6 characters of the basename a numeric tail ~n, where n is a digit. For example, a file called ALongFileName.LongExtension will get a short alias alongf~1.lon. When you then reboot into plain DOS, your programs will see this short version only, which will almost certainly break them, since, when a program running under DOS asks for a file with the above long name, DOS transparently truncates it to alongfil.lon, and such a file does not exist. Disabling the numeric tails forces Windows not to use numeric tails unless there is another file in the same directory whose short alias clashes with that of the new file. If no such clash happens, Windows will simply truncate the long name as DOS would, which is exactly what you want.

Here is how you disable the numeric tails on Windows 9X:

As an alternative to running regedit, you can create a file named, say notail.reg (the name is arbitrary, but it must have a .reg extension), with this content:

REGEDIT4

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\FileSystem]
"NameNumericTail"=hex:00

then double-click on the name of this file in Explorer or My Computer. Windows will then run regedit for you. You still need to reboot the machine afterwards.

If setting NameNumericTail to 0 breaks some programs, you can restore its original setting temporarily, while you run those programs. NameNumericTail only affects the short names of new files being created, it has no effect on the files that already exist.41

Besides the numeric tails, you need to make sure any files and directories you create have unique 8+3 aliases which are true truncations of the long names to 8+3 limits. This means that you should avoid file names with leading dots, such as .emacs and .bashrc, file names with more than a single dot, like make-3.77.tar.gz, or file names which include characters not allowed by DOS, like libg++.a.

One other problem is to avoid using programs which create numeric tails even if they are disabled in Windows. One such program is pkunzip version 2.50. Don't use it, if you want to keep your dual DOS/Windows installation in working order.

The most simple method of deciding at boot time which configuration (DOS or Windows) to start is to edit the (hidden) file MSDOS.SYS, which is a text file in Windows 9X, and force the Windows boot process to present a menu where one menu item, called "Command Prompt Only", allows you to start DOS 7 without the Windows GUI. To this end, change the line of MSDOS.SYS that reads "BootMenu=0" to say "BootMenu=1" instead, and reboot. Since MSDOS.SYS is a hidden file, you will need to remove the hidden attribute from it before you can edit it; use the ATTRIB command for that.



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  Copyright 2001   by Eli Zaretskii     Updated Apr 2001