DEF File

What are DEF files and how to open them

Are you having problems opening a DEF file or just wondering what they contain? We explain what these files are used for and show you software that we know can open or otherwise handle your files.

What is a DEF file?

DEF files have multiple uses, and 22DISK Format Definition is one of them. Read more about the other uses further down the page.

22DISK Format Definition File

We have not yet analyzed in detail what these files contain and what they are used for. We're working on it.

How to open DEF files

Important: Different programs may use files with the DEF file extension for different purposes, so unless you are sure which format your DEF file is, you may need to try a few different programs.

While we have not verified the apps ourselves yet, our users have suggested ten different DEF openers which you will find listed below.

Last updated: January 19, 2023

All known file formats using extension .DEF

While 22DISK Format Definition File is a popular type of DEF-file, we know of 6 different uses of the .DEF file extension. Different software may use files with the same extension for different types of data.

Module-Definition File

Files that contain the .def file extension are most commonly associated with Microsoft Visual C++ definition files. These files list the exports and attributes of a specific program that is linked by an application linker.

The DEF file format is commonly used when creating a dynamic link library during the development of a software application.

DEF opener for Windows

We have identified one DEF opener that is compatible with this specific type of DEF file.

More file formats using the DEF extension

Through our research of DEF files, we know that the following formats exist. However, we have not yet analyzed them in detail.

  • Chinese UCDOS Print Definition File
  • Personal Font Maker Definition File
  • Philips Ease Database Definition File
  • ThunderByte Antivirus Definitions

Various apps that use files with this extension

These apps are known to open certain types of DEF files. Remember, different programs may use DEF files for different purposes, so you may need to try out a few of them to be able to open your specific file.

Army BuilderArmy BuilderUser submitted
progeCAD ProfessionalprogeCAD ProfessionalUser submitted
Movie Magic ScreenwriterMovie Magic ScreenwriterUser submitted
WinEdtWinEdtUser submitted
MapBasicMapBasicUser submitted
UntisUntisUser submitted
Open WatcomOpen WatcomUser submitted
Evaluation FlashEvaluation FlashUser submitted
IrfanViewIrfanViewUser submitted
ABCreator for Army BuilderABCreator for Army BuilderUser submitted

Help us help others helps thousands of users every day, and we would love to hear from you if you have additional information about DEF file formats, example files, or compatible programs. Please use the links below or email us at to discuss further.