D1M File

What are D1M files and how to open them

Are you having problems opening a D1M 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 D1M files.

What is a D1M file?

A .D1M file is a CMD FD Serie Disk Image file.

CMD FD Serie Disk Image files represent complete dumps of floppy disks used by CMD FD-2000 and FD-4000 disk drives, third-party devices made for Commodore 8-bit computers. These image files preserve every sector of a floppy formatted in CMD's native CMD partitionable format, including DOS headers, block allocation maps, directory structures, and all content needed to mount them as if the original physical disk were inserted.

Such a disk image appears when the CMD FD drive is used with its utility programs (such as CMD's FD-TOOLS) to format a floppy disk in native mode at various densities (double-density, high-density, or enhanced density), then the drive's full disk contents are copied sector-by-sector into a file. Emulation software and tools for the Commodore 64/128 (for example VICE and OpenCBM) use these images so that unmodified software, including GEOS and CBM DOS programs, run exactly as with the hardware, including read/write operations and full directory support. CMD FD-2000 supports 1600 KB in HD and CMD FD-4000 supports 3200 KB in ED, retaining support for the original 800 KB DD format. This type of image differs from simpler 1581 or 1541 images in having more sectors, larger sector size in many cases, and ability to contain partitions and subdirectories.

The size of a correctly formatted image depends on density and format: a DD image for an 81-track, two-sided CMD FD-2000 disk uses around 829,440 bytes; the HD image about 1,658,880 bytes; and the ED image for FD-4000 about 3,317,760 bytes. These images map physical track count (usually 80 tracks numbered 0-79, both sides), sector counts per track, and logical filesystem metadata (labels, IDs, directory hierarchies) according to CMD's specification. Tools like libcbmimage support these image types under the names D1M (DD), D2M (HD), and D4M (ED) for image variants.

These image files can often be identified by internal signatures such as the presence of the ASCII strings "CMD FD SERIES" and "SYSTEM", along with byte patterns at the start of the image file matching CMD's system partition header layout. The byte signature often shows long regions of zero bytes followed by structured data reflecting the system partition, disk label, DOS type "H", version "1H", track/sector references to directory blocks, and other filesystem metadata placed at known offset locations.

How to open D1M files

Important: Different programs may use files with the D1M file extension for different purposes, so unless you are sure which format your D1M 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: September 21, 2026

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