Get Cozy With BlueSCSI

For a while now, a go-to solution to replace mechanical SCSI hard drives was the SCSI2SD. It’s still a great way to add high capacity storage to a vintage Mac – but now there’s a new kid in town, the BlueSCSI. This post covers what makes the BlueSCSI special, and a strong contender to replace your classic machine’s mechanical drive.

BlueSCSI on an LC III


The premise is very similar. The BlueSCSI is a new device that allows you to use a modern SD card as storage on your retro machine. That’s about where the similarities to SCSI2SD end though! The SCSI2SD directly exposes the partitioned SD card to the Mac, whereas the BlueSCSI actually allows you to store drive images on the SD card. Instead of setting up fixed partitions and flashing data to the device, all that is required of the BlueSCSI is drive images saved to the SD card. It’s fairly plug-and-play.

The advantages to this is you can very quickly make new drives, copy drives to a newer computer, download full working drives, transfer data between vintage machines, or use it to mount ISOs as a virtual CD-ROM drive. This opens the door to much more experimentation, allowing you to try out different OS versions and so forth.

Blue to You

The BlueSCSI’s name comes from the BluePill Arduino board that it’s built on. The hardware and software is open-source and developed by enthusiasts. You can build one from a kit or order one fully assembled, even in a 3d-printed case. Check out https://scsi.blue/ for more.

I ordered mine pre-assembled, in a 3d-printed case. I also selected one that could be used externally so I could quickly move from one classic Mac to another. If you’re interested, I ordered mine from Kero’s Mac Mods which did an amazing job assembling and shipping the product. This vendor and many amazing others are found on the Scsi.Blue site.

Creating drives on BlueSCSI

Now that you know what it is, and where to get it, let’s talk about using the BlueSCSI. It’s actually dead simple.

The BlueSCSI will scan the root level of an ExFat formatted SD card, looking for drive images that follow a simple naming convetion:

"HDx somename.hda" or "CDx somename.iso"

In the above, the filenames start with either HD or CD to determine hard disk or CD drive. X is the SCSI id. This provides a name like “CD4 Myst.iso” or “HD4 RetroGames.hda”.

There are actually more settings beyond this if you need them, but they are completely optional. You can specify a LUN id directly after the SCSI id, making a name like “HD40 Spiffy.hda”. Furthermore you can specify sector size after an underscore like: “HD50_512 Example.hda”

Note: I’ve noticed you get warnings in the log file sometimes if you do not provide a value for LUN id. I include the 0 just to keep things cleaner…


Performance is an interesting topic. These days we associate solid state devices with high speeds, and I ran under the assumption that the SD would be a faster medium than a 30+ year old mechanical hard drive. But then I watched this YouTube video about the BlueSCSI. In it, the BlueSCSI is benchmarked against the SCSI2SD and the original mechanical drive – and to my surprise, it came in dead last. I also replicated this claim using DiskBenchmark and SCSI Director Pro.

Now given that information, you might not actually notice a perceivable difference on an older Mac which might experience other performance bottlenecks. Plus the PROs far outweigh the CONs with a device like BlueSCSI. Mechanical drives from the 80s and 90s are becoming more and more scarce and they are all prone to fail over time. But you have to make the call for yourself ultimately.

In my humble opinion, I think the SCSI2HD still stands as a rock-solid solution for an internal hard drive replacement. In some testing, it outperforms the BlueSCSI. It is harder to set up though, so it fits nicely as a “set it and forget it” type solution. The BlueSCSI is perfect as an external device that you offers flexibility and ease of use. Plus, the added benefit of playing the role as a virtual CD-ROM drive.

Tips & Tricks

  • The BlueSCSI only scans the root of the drive, meaning you can make folders and store images that you want to swap out temporarily – or backup. You could keep a folder of zip’d blank drive images to quickly spin up new drives.
  • On the scsi.blue site, there are links and resources to sample drive images, images with OS installations, and bundles of apps and games to try out.
  • There’s a log file automatically generated when the BlueSCSI powers on – so you can troubleshoot problems (for example, an invalid image or conflict.)
  • I keep a text file in a folder that lists notes for which machines are using which SCSI IDs for organization.
  • The coolest trick of all might be the following. You can use the .HDA disk image files in the emulator BasiliskII! Open settings and point to the file – and presto! (More on Emulators here!) See screenshot below…

I’m Blue / Gotchas, Etc

  • Remember SCSI termination
  • Remember the Mac reserves ID 7 for the machine. Often 0,1, and lower numbers are used for internal drives. 4 and 5 often were used with external Zip and CD drives back in the day. (Some had switches and only allowed for values like that)
  • For use on the Mac Plus – there is an extra assembly step required.
  • Filenames for drive images have a max length of 64
  • For CDs, don’t forget to run CD-ROM drivers, including all of the helper extensions that go along with it. This isn’t as straightforward as you might assume, but many pre-built drives with OS installations have them ready to go.
  • Remember that classic Macs store the startup disk selection in PRAM, so you will need to select this frequently in Control Panels when changing volumes around. SystemSwitcher is a good option to manage this. You can also force the Mac to boot using a SCSI id with a keyboard combination on startup: CMD+OPTION+SHIFT+DELETE+# (where # is the SCSI id)

Final Thoughts

The BlueSCSI is insanely cool. It’s flexible and easy to use; just drop drive images on it and before you know it, you’re up and running on your vintage Mac. The possibilities are endless. It’s a great way to try out A/UX without “committing to it” or simply moving files from one machine to another. (Including to a newer machine via mounting the drive image in BasiliskII)

If you’re ready to take the plunge into the deep blue SCSI, check out the official site (Scsi.blue) – it contains excellent resources for getting up and running, along with links to sample drive images.

Thanks for reading, and have fun!