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One problem with working with computers that date back to the 80s and 90s is that hardware failures become more and more common. One device in particular that is prone to failure in older machines is the mechanical hard drive. Finding new hard drives for these older SCSI-based 68k Macs can be challenging – but fortunately there’s a better option out there today!

Put simply, the SCSI2SD is a device that lets you use SD cards in your older mac as if they were normal hard drives. The device works in pretty much any SCSI-based Mac and is often many times faster than the older mechanical drives. There are other benefits too such as reduced noise, reduced heat, higher storage capacities, and an overall smaller form-factor.

The SCSI2SD can be a little tricky to get set up, especially if you haven’t used SCSI devices in recent times. SCSI can be somewhat nuanced – so let’s start off with a little background on SCSI. If you’re familiar with SCSI – feel free to skip the next paragraph!

What is SCSI?

SCSI, or small computer system interface, allows users to chain 8 devices up on a “bus”. SCSI chains must be terminated at both ends of the bus. On 68k Macs, a typical scenario would be a Mac that is internally terminated, a hard drive (usually ID 0) and possibly external SCSI devices such as Zip/CD/external hard drives. The system will use ID 7, meaning the other devices end up with IDs such as 4,5,6, etc. The Mac won’t operate if two devices share the same ID, or the bus isn’t terminated correctly… so getting everything just right is key.

In troubleshooting SCSI-related problems a program such as Mt.Everything or SCSI probe is quite useful.

Before you start

Once you get your hands on the SCSI2SD and an SD card, there are a few considerations to make before installing…

  • First off, ensure you have a way to re-install your OS and move any files off your older drive. One option here may be to simply add the SCSI2SD on an internal ribbon cable along side the existing hard drive – as long as they have unique SCSI IDs. You could also use an external drive casing as a makeshift adapter.
  • Decide if you are going to want to change the SD card, or use the USB port once the device is installed. I have seen some examples where people use a USB extension cable to provide access to the drive on the rear of the Mac.
  • How is the drive going to be physically mounted? It’s smaller than a normal hard drive, so you may find yourself needing an adapter – or drilling out new holes in a hard drive sled to mount it.
  • Depending on your system’s configuration – The SCSI2SD may run right off of the SCSI bus power – meaning you don’t necessarily need to plug a power cable into it. If you do need to supply power it to it (or just want to) you will most likely want to use a 4-pin molex to 4-pin floppy adapter.
  • The SCSI2SD comes in different versions depending on your needs. The version I have used and will be referring to is v5. If you don’t feel comfortable opening a Mac up and replacing an internal drive they also make a version that is designed to be used externally – like an old external hard drive.
  • In the next section, I’ll cover the set up process. Macs before System 7.5 can only use up to 2GB drives – so you would need to either set the device up this way, or partition the drive. Higher versions of the Mac OS will be able to read larger drives. You may even want to create several drives on the SCSI2SD so you can install multiple versions of the OS. It’s all a matter of your preference.
  • Don’t forget to use all safety precautions associated with working on these old systems! Read all warnings before proceeding. Do any work at your own risk!

Setting up the SCSI2SD

The SCSI2SD can be configured using the software provided here…


Using a newer computer, download the software and connect the SCSI2SD via a USB cable. The software should detect the presence of the device and allow you to read and write configuration to the device. It’s worth noting that the device itself contains the configuration – not the SD card.

There are various things that need to be configured. In selecting your settings remember the SCSI devices needs to all have unique IDs, and the bus needs to be terminated. Depending on what other devices you will be using on your Mac, these settings will vary. The SCSI2SD can emulate 4 different SCSI devices which map to regions of the SD card storage. The Mac will see these as up to 4 distinct drives can be then partitioned further if needed.

Above, I’ve included screenshots of sample settings that I’ve used for a PowerMac 7600 w/G3 card. This was for an internal hard drive replacement with a single, large 16gb volume running OS9. The big points of interest above are: I’ve turned off termination, set SCSI2 mode (for a little extra performance), and then configured Device 1 with settings I’ll expand on in the next section.

Here’s another (more complicated) example. These above screens shows configuration for my mystic-upgraded Color Classic (so, LC 575 / Performa 575 essentially.) What I’ve done here is made several “smaller” drives so I can run multiple versions of the system software. Specifically, drives 1 & 2 are 2 GB each and drive 3 uses the remaining 12 of the SD card. I’ve partitioned the large 12 GB drive making two smaller volumes for even more flexibility. For reference, included is a picture of the Mac running Mt.Everything showing my SCSI bus with the SD drives, along with an external Zip drive.

A few final tips on managing configurations. First off, the SCSI2SD software will load the defaults when you open it. If you want to make changes to the configuration currently on the device, be aware you have to manually load it. It’s also worthwhile to save a backup of working configuration – in case you ever need it.

Formatting the SCSI2SD from the classic Mac

Of course, nothing’s simple! The older Mac drive setup programs were originally designed to only work with drives that Apple officially supported. This gives us two options to work with:

  • Disguise the SCSI2SD as a supported drive (see below)
  • Hack the drive setup program with a patch to allow it to format un-supported drives. Download the patch here.

Both methods work, but may take some trial and error. Also be aware that different versions of the drive setup application will install different versions of disk drivers which can cause a headache if you’re not careful.

In terms of “disguising your drive” – this comes down to setting the vendor, product ID, and revision settings to a supported manufacturer – which there are several to choose from. I have had the most luck with:

Vendor: " SEAGATE"
Product ID: "          ST225N"
Revision: "1.0 "

Note these text values are specifically padded with extra spaces!!

More tips and tricks

  • When starting up, you can hold down CMD + OPTION + SHIFT + DELETE +# to boot from a specific SCSI ID #
  • You can actually take the SD card and mount it on a newer Mac and view it’s contents. This is a great way to back up old media onto a newer system.
  • You can attach an LED light to the SCSI2SD for drive activity indication

Where to get a SCSI2SD: