CDC File

What are CDC files and how to open them

Are you having problems opening a CDC 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 CDC files.

What is a CDC file?

CDC files have multiple uses, and Chaos Compacted Disk Image is one of them. Read more about the other uses further down the page.

Chaos Compacted Disk Image

Chaos Compacted Disk Image is an Atari ST disk image format written by Miles Vignol in the program called Chaos Disk Compacter (CDC). It packs the entire contents of a floppy disk - including all its sides, tracks and sectors - into a single compressed file. The purpose is to back up disks to hard drive, send disk images over modems, or archive whole disks when physical media is unavailable.

Creating this format is done using the CDC software on an Atari ST. CDC reads every readable sector from a floppy disk, applies two compression stages - first a custom run-length encoding step called Packing, then a dynamic Lempel-Ziv-Welch scheme called Squashing - and writes the result into a Chaos Compacted Disk image. When decompressed, CDC will reconstruct the original disk layout into a blank disk, optionally formatting or using write-verify where needed.

Files using this format begin with a text signature at the very start: bytes at offset zero read as ASCII "ChaosCompactedDisk\r\n" (that is, the characters C h a o s C o m p a c t e d D i s k followed by a newline and carriage return).

How to open CDC files

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

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

Last updated: August 31, 2026

All known file formats using extension .CDC

While Chaos Compacted Disk Image is a popular type of CDC-file, we know of 2 different uses of the .CDC file extension. Different software may use files with the same extension for different types of data.

Telvox CODEC Archive

We know that one CDC format is Telvox CODEC Archive. We have not yet analyzed in detail what these files contain and what they are used for. We're working on it.

Various apps that use files with this extension

These apps are known to open certain types of CDC files. Remember, different programs may use CDC 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 CDC file formats, example files, or compatible programs. Please use the links below or email us at submit@file.org to discuss further.