CoCo SDC – compatible disk controller using SD cards

10/20/2014 Update: They made more! Ed Snider is producing them with Darren’s permission. Contact him at

12/12/2014 Update: Tim Lindner is making plexiglass enclosures for the CoCoSDC, too (in case you don’t have a dead FD502 cartridge to repurpose).

Update: The first run of these packs was sold out, and no more are available unless they decide to make more later. As a hobby project, these were being hand assembled as a fun project. Still, it’s a very interesting project to read about.

A project that I mentioned last year in my CoCoFEST! report has made it to distribution. The CoCo SDC project by Darren A. is designed to plug in to a Tandy/Radio Shack TRS-80 Color Computer (CoCo) cartridge port and act like a floppy drive controller. Instead of hooking up old 5 1/4″ or 3.5″ low density floppy drives, the device uses an SD memory card. Disk images can be placed on the card, and then the CoCo doesn’t know the difference. This is huge, since it provides the first nearly 100% compatible virtual drive experience the CoCo has ever had.

Every drive replacement solution over the years, including the original “most compatible” RGB-DOS for hard drives, only worked with programs that used DISK BASIC calls to do the disk I/O. This eliminated many games that did their own disk I/O for speed or copy protection. Also, even the virtual floppy drive system of RGB-DOS (and later modifications, such as HDB-DOS from Cloud-9) had drawbacks. While it might be possible to have 255 virtual floppies on a CoCo, and the system allowed doing things like “DIR 201” to access higher drive numbers, most CoCo software only expected drive numbers 0-3. Multi-disk programs might expect the main disk in DRIVE 0 and the second disk in DRIVE 1. None of these could work directly without physically being on those drives, or having the software patched.

CoCo SDC solves this by simply presenting virtual disk images as drives 0-3. Extensions to DISK BASIC allow selecting the file and on which drive letter it should appear as a valid floppy.  Very clever.

Swapping out virtual disks is done using DISK BASIC commands (extended to support this).

Check it out today:

3 thoughts on “CoCo SDC – compatible disk controller using SD cards

  1. Keith Clark


    Do you have contact information for the producers of this board? I’d love to put myself on a waiting list, just in case they do decide to make more.




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