Illegal Windows Names

Written by Eric Wyatt (last updated November 2, 2020)

There is a lot of things we are able to do with our computers, especially with the Windows operating system. As the years go by we gain more and more features, faster and easier ways of doing things. Gone are the days of needing to swap out floppy disks.

Even with the advances in features, some things remain constant. One of those constants for the Windows operating system dates back to MSDOS and has to do with naming files. Due to the continuation of Windows being built on its predecessors, things that were not allowed, or illegal, tend to continue being unallowed. Even if things are not done the same way now they have to continue the tradition due in part to two words—backward compatibility. One of the areas where this is the most prevalent is, as mentioned before, with regards to naming a file or folder on your computer. If you try to use certain names, Windows simply won't allow it. You will get a simple dialog box that says "The specified device name is invalid." (See Figure 1.)

Figure 1. Rename dialog box showing a name can't be used.

Try as hard as you might, Windows will not allow these names for files or folders on your system:

CON COM4 LPT3
PRN COM5 LPT4
AUX COM6 LPT5
NUL COM7 LPT6
COM1 COM8 LPT7
COM2 COM9 LPT8
COM3 LPT1 LPT9
  LPT2

That is it, those are the names that cannot be used for files or folders on any Windows system. As you try to name your files keep these in mind, so even if it makes sense to you to put all of your Corporate Office Newsletters in an abbreviated "CON" folder you can't, and you'll need to come up with a new name. If you want to know about illegal characters check out this tip on character limits.

 This tip (13797) applies to Windows 7, 8, and 10.

Author Bio

Eric Wyatt

Eric Wyatt is a swell guy (or so his friends tell him). He is a formally trained designer and branding expert, bringing a wide range of skills to his Tips.Net articles. ...

MORE FROM ERIC

Turning on Inactive Window Scroll

Have you ever needed to scroll through an inactive window while keeping another window active? This tip will show you how ...

Discover More

Launching and Understanding the Xbox Game Bar

The Xbox Game Bar is a feature that often goes unnoticed by non-gamers. Let's go over launching and default settings for ...

Discover More

Finding Large Files

Large files can quickly take up valuable space on your hard drive. In this tip you discover how to easily search for ...

Discover More
More WindowsTips

Sorting a Folder

When you have a lot of files in a folder, it is helpful to be able to know how to sort through all the files. Windows 10 ...

Discover More

Finding Large Files

Large files can quickly take up valuable space on your hard drive. In this tip you discover how to easily search for ...

Discover More

Specifying a Copy Schedule in Robocopy

There are a few ways to set up a copy schedule in Robocopy by using its options. This tip explains how.

Discover More
Comments

If you would like to add an image to your comment (not an avatar, but an image to help in making the point of your comment), include the characters [{fig}] (all 7 characters, in the sequence shown) in your comment text. You’ll be prompted to upload your image when you submit the comment. Maximum image size is 6Mpixels. Images larger than 600px wide or 1000px tall will be reduced. Up to three images may be included in a comment. All images are subject to review. Commenting privileges may be curtailed if inappropriate images are posted.

What is two more than 4?

There are currently no comments for this tip. (Be the first to leave your comment—just use the simple form above!)

Newest Tips
Links and Sharing
OUR COMPANY
OUR PRODUCTS
OUR SITES
 

Copyright © 2026 Sharon Parq Associates, Inc.