Lead with Knowledge

Learn to secure your PCs from new and unknown hacker attacks.

Free IDC White Paper - Discover Secure File Sharing for the Enterpriseattacks.

Home  //  Article
Print Article    Email Article
Window Manager
Brian Livingston
Why I accept no subst

I PRINTED a reader's tip a few weeks ago about making a folder look and act like a drive letter. This can be handy when an application demands that a CD be specified using a drive letter (even when you've copied the CD into a folder) or when you want to operate on a folder without spelling it out (when burning a CD-RW, for instance).

Such a "virtual" drive, reader Anthony Cimorelli noted, can be created in Windows 2000 by sharing a folder, and then pulling down the Tools menu in Windows Explorer and clicking Map Network Drive to assign the folder, say, to the letter V (see the April 2 Window Manager). This also works in some older versions of Windows.

Several readers wrote to say that file transfers to a virtual drive created in this way are slower than transfers to a virtual drive created using the DOS command Subst. In addition, John Eccles writes, the default settings for a shared folder give access to everyone. This can be changed easily but might not be apparent to novice users.

Because mapping has an easy graphical user interface, I didn't want to drag in the Subst command and clutter up Cimorelli's 100-word tip. But since several readers have expressed a keen interest, let me take you behind the mystic veil into the occult realm of the DOS command line.

Subst has a troubled history. If you used Subst in DOS 5.0 to create a virtual drive, the setup routine for Windows 3.0 would crash. This was fixed in Windows 3.1, but then graphical applications would fail. In addition, Subst wasn't compatible with commands such as Backup, Chkdsk, and others.

These problems have largely been fixed in the command-line utilities that come with more recent operating systems, such as Windows 2000. But there are still enough "gotchas" that other methods may be preferable.

Using Subst is easy enough. You open a DOS window, and then type SUBST V: C:\foldername to create a virtual drive letter V. But look out for the command's quirks.

Not accessible. You can use Subst to associate a drive letter with a network resource using a UNC (universal naming convention) path. But when you access the virtual drive in Windows 2000's Windows Explorer and My Computer, you'll get an error message (for more information, see article Q246887 at

No removal. If you're using a domain user account in Windows 2000, you'll get an "access denied" message when you try to delete (undo) a virtual drive with a command such as SUBST V: /D. This is due to security restrictions (see article Q258625).

Fallacious red X. Windows 2000's My Computer may display a drive letter created with Subst as a disconnected network drive marked with a red letter X, although you can in fact access the drive (see Q269163).

Spoofing. Because Subst is persistent for all users who log on to the same computer, it's possible for one user to "spoof" or impersonate another user's drive letter (see Q265351).

This problem is fixed in Microsoft's recent Service Pack 2 for Windows 2000. The service pack, which was released on May 16, is a superset of all the fixes that were in Service Pack 1, so there's no need to install SP1 before installing SP2. In addition to the spoofing problem, SP2 patches a variety of issues, including an assortment of memory leaks and incompatibilities. (For the complete listing, and information on how to download and install SP2, see Q260910.)

If you wish to play with the command line at all, you may be better off using the Net command to create virtual drives. For instance, the command NET USE * \\servername\share\path1\path2 assigns the next available drive letter to the specified folder.

Neither Subst nor Net will execute in the Autoexec.nt file under Windows NT or 2000. Instead, you must use a batch file in the StartUp group or a user's log-in script (see Q129128).

Reader Eccles will receive a free copy of Windows 2000 Secrets for being the first to send me a tip I printed.

Backup Web server for CacheSentry

I recommended a few weeks ago a free program called CacheSentry to clean up files left over by Internet Explorer and Outlook Express (see the May 14 Window Manager). apparently limits the megabytes that can be downloaded each month from its users' personal Web pages. So if you couldn't download CacheSentry from there, use instead the mirror server at

Go ahead, make my day

I recently revealed a little-known Registry setting in Windows 2000 that can save you 30 seconds every time you view shared files across a local network (see the March 12 Window Manager).

Reader Bill Edmison reported in's Windows newsletter the results he got from this change: "I can now access all 13 computers on our network instantly instead of waiting 35-40 seconds for each." That's exactly the kind of feedback that makes it all worthwhile.

Get Livingston free via e-mail

Go to and click Window Manager or E-Business Secrets to receive either of Livingston's weekly columns.


Operating Systems

SUBSCRIBE TO:    E-mail Newsletters  InfoWorld Mobile InfoWorld Magazine
Home  //  Article Print Article    Email Article
Back to Top


Gateway: Your Reliable IT Provider of Business Technology Solutions
Learn to secure your PCs from new and unknown hacker attacks.
Get FREE Hurwitz Report: Control Your App Dev Costs with TogetherSoft!
Click here to receive a FREE Success Kit from Oracle.

E-mail Newsletters
InfoWorld Mobile
Print Magazine

Web-based training

Copyright 2001 InfoWorld Media Group, Inc.