DC42 File

What are DC42 files and how to open them

Are you having problems opening a DC42 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 DC42 files.

What is a DC42 file?

A .DC42 file is a DiskCopy 4.2 Disk Image file.

DiskCopy 4.2 Disk Image files are floppy-disk images created by Apple's Disk Copy version 4.2. These images are exact sector-level copies of 3.5-inch floppy disks from classic Macintosh and Apple II machines. Each captures all data sectors and, optionally, "tag" bytes (extra metadata stored per-sector on some Apple-format disks), making them suitable both for archival purposes and for precise duplication of disk contents. The format does not include compression or sparse block optimization, and it was designed specifically for floppy disks.

Files in this format are produced by the Disk Copy 4.2 utility. The workflow is that one uses Disk Copy 4.2 (on a Macintosh or compatible system) to read an existing floppy disk into this image format, or to duplicate floppy disks by writing out a DiskCopy 4.2 image to physical media. Third-party tools and emulators also support reading DiskCopy 4.2 images, converting from or to raw disk formats.

Internally, a DiskCopy 4.2 image begins with a header roughly 84 bytes long: it stores the image's name (ASCII, padded), a big-endian 32-bit count of the data bytes, a 32-bit tag byte count, checksums for data and tags, a byte indicating disk encoding (e.g. GCR or MFM), a format byte, and a 16-bit fixed "magic" word (0x0100) to identify the format. After the header, the actual disk data sectors follow, and if tag data is present, that is stored at the end.

How to open DC42 files

Important: Different programs may use files with the DC42 file extension for different purposes, so unless you are sure which format your DC42 file is, you may need to try a few different programs.

We have not yet verified any programs for Windows that work with this specific file format. If you know one, please use the 'Suggest a program' link below. Thanks!

Last updated: October 22, 2026

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