CMU File

What are CMU files and how to open them

Are you having problems opening a CMU file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your CMU files.

What is a CMU file?

CMU files have multiple uses, and Andrew Toolkit Document is one of them. Read more about the other uses further down the page.

Andrew Toolkit Document

These CMU files are documents created in Andrew Toolkit, a set of tools used to create documents. Andrew Project was one of the first distributed computing solutions, and it provided students and teachers access to various software on computers placed on the university campus. It was developed by Carnegie Mellon University and IBM in the 1980s.

How to open CMU files

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

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

Last updated: August 31, 2026

All known file formats using extension .CMU

While Andrew Toolkit Document is a popular type of CMU-file, we know of 2 different uses of the .CMU file extension. Different software may use files with the same extension for different types of data.

CMU Window Manager Bitmap

CMU Window Manager Bitmap is a format used by an early window manager developed at Carnegie Mellon University, intended for storing monochrome images - icons, bitmaps, or masks - that the window manager displayed. It provides a simple way to represent black & white (1-bit-per-pixel) images for UI decoration or control elements, allowing them to be converted into or out of more general bitmap formats for display or editing.

The Netpbm toolkit supports two related conversion utilities: cmuwmtopbm and pbmtocmuwm. The first reads a CMU Window Manager Bitmap file and writes a portable bitmap (PBM) image. The second reads a PBM image and produces a CMU Window Manager Bitmap file. These tools treat the format as uncompressed, entirely monochrome, without color depth beyond 1 bit per pixel.

No detailed public specification of the binary layout (headers, padding, pixel order) has been located in primary sources that match precisely the byte signature associated with the format. The format is recognized by a byte signature beginning with the bytes F1 00 40 BB 00 00 at offset zero.

Various apps that use files with this extension

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

Help us help others

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