USB or FireWire to SCSI for Macs

Most recent revision for this page dated June 14 2010 On this Web page I describe a USB to SCSI conroller, and how a customer connected his G5 Mac to his older Mac's SCSI drives. Most photos and the description of methods are courtesy of Joe Hunt. I also mention FireWire to SCSI adapters. - Herb Johnson.

To return to my Mac SCSI drives page, follow this link.


In Feb 2008, a customer named Joe Hunt contacted me about connecting his older Mac's SCSI drives to his G5 Mac. Like most modern Macs, it does not have a SCSI controller to operate SCSI drives, it uses "IDE" or "ATA" type drives. The older Macs of the 1990's and earlier used SCSI drives. I told him I don't offer USB to SCSI products, so he looked around the Web and found such a product. Joe came back to me, to provide an external case for his SCSI drives which would have physical connections to match the USB to SCSI controller's SCSI-2 connector. He then successfully connected his G5, the USB to SCSI controller, the case and his SCSI drive.

What I sell for SCSI drives

I provide external SCSI drive cabinets on this Web page. That page also has SCSI hard drives, ZIP drives, and CD-ROMS, and brief discussions about these devices. A more technical SCSI Web page is at this Web page which has more technical information. As of Feb 2008, I don't provide the USB to SCSI controllers or devices; I can't buy them cheaper than YOU can, so I can't sell them at a competative price. Find them on the Web.

USB to SCSI conroller and issues

The controller he found, was as he put it, "a USB to SCSI 2 CABLE - IOMEGA Jaz, reseller is no name brand. In fact the one I bought had stickers over the IOMEGA. The [software] disk supplied for it was for [a Windows-type] PC, not MAC.". Here's an image of the device.. I've seen such devices for sale on Internet auction sites and by some Web-based computer product vendors; a Web search like "USB to SCSI controller" will find some available, for well under $100 as of 2008.

The SCSI end of the controller has a SCSI-2 "male" connector; that connects to a SCSI cabinet with a complimentary SCSI-2 "female" connector. Inside the cabinet, the SCSI-2 connectors are on a cable with a 50-pin connector which mates to the SCSI-1 type drives used in most older Macs. Here is a photo of the back of the SCSI drives which shows their connectors. The drives also need DC power, and the cabinet has an A/C power supply to provide the power through standard DC power connectors. Those are the four-pin connectors also shown on the back of the hard drives.

There are issues about setting up SCSI hard drives. ONe issue is called "SCSI address" or "SCSI ID". A SCSI controller can connect to and control ONE to SEVEN other SCSI devices, so each one must have a unique "address" from zero to six. "Addressing" is determined by jumpers on the SCSI device. The other issue is called SCSI "termination", which is something needed when you connect one or more SCSI devices to a SCSI controller. It's done on the LAST device at the far end of a chain of SCSI devices, or the ONLY device. I discuss these considerations on my Mac drives Web page.

Another issue is a software issue called "drivers". Macs and Windows PC's have pieces of software which are either part of the operating system (Windows or OS X) or which are provided with devices you add to your computer. That software allows and supports the operating system to communicate and use the added device. Then software programs you run, can use those and other devices on your Mac in a consistent and correct fashion. All this is generally automatic for NEW devices you add. When you add "old" stuff, like SCSI drives on a G5 Mac, OS X (or your particular operating system) may or may not "expect" those devices, and not know how to use them, unless you find and "install" a device driver. ("Drivers" for Windows will not work with OS X or OS 9 on Macs; drivers for OS 9 will not likely work with OS X.)

Joe came up with a method which seemed to work, to resolve these issues. He did not seem to have problems with software drivers. I suggest you review the information you get with your controller; the information linked above; the information below. But I make no warrenties whatsoever that all this information is correct or complete. Use this information at your own risk. I am not responsible for any loss, injury or damage of any sort.

Methods for use

From Joe Hunt:

The configuration of the external drive went like this:

COMPUTER to (USB to SCSI 2 cable) to (peripheral box SCSI2 external to SCSI internal)

The USB to SCSI 2 CABLE - IOMEGA Jaz, reseller is no name brand. In fact the one I bought had stickers over the IOMEGA, disk supplied for PC, not MAC. MAC G5 (OSX 10.4.10) had no trouble mounting the Jaz USB module without a supplied driver.

INSTALLING HARD DRIVE to peripheral box.

I had read when trying to mount a SCSI drive this way to set the drive to 0, Termination seems to be dependent on drive manufacturer. Set drive to 0 and connect drive to box SCSI cables


Power up box and plug in USB - if drive does not spin up, unplug USB and power down

ry adding termination jumper - Power up and plug in USB - if drive spins and does not mount - unplug USB and power down


check SCSI ID again - move jumper to new position - power up box and plug in USB - if drive spins and does not mount - unplug USB and power down - repeat

NO JUMPER METHOD: Remove all jumpers - power up and plug in USB

Using a combination of these methods worked for me on 3 different drive manufacturers, by process of elimination. - Joe Hunt

Another customer's experience with USB SCSI

Text below by Edward Schmidt during April 2008, used with permission. Ed had a 2.5" SCSI drive from a Powerbook 140, a model "Conner CP2045". I told him to get a 2.5inch SCSI laptop drive adapter card. It's a circuit board that converts to a full sized SCSI connector, as is on 5.25 inch SCSI drives. Then you can connect that to some external SCSI box and access that box. Those adapters are sold by many vendors on the Web. Search for [SCSI 2.5" drive adapter] to find one.

I had two USB-SCSI converters; one from Ratoc, another from Xircom. Found both on eBay. First I tested both with known good SCSI drives. The Ratoc worked out of the box on OSX 4 (no drivers needed), though the adapter required an external 5V supply (not included) to work; the Xircom only worked on XP (not on OSX), and then only after forcing XP to install the NT drivers.

My old PowerBook drive was sufficiently broken that none of the utilities I tried on OSX or XP would mount or recover it, so I burned this Linux CD

and used that to boot my Mac. Strangely, under Linux, only the the Xircom converter (which hadn't worked at all under OSX) would recognize the drive.

"ddrescue" is a utility on that boot CD, and was able to do a block-by-block clone of my bad drive to an image file on a separate (FAT32) hard drive I had plugged in and mounted. Then OSX was able to fix and mount that image file, and my old documents were all there.

[Regarding setting the SCSI address of the laptop drive.] The 2.5" drive doesn't have visible jumpers, but they're on the drive adapter card [I purchased seperately]. So I just hooked up the jumper lead from the enclosure to that card and it seemed to work. I left the id at 0 and everything worked fine.

The ddrescue utility doesn't recover individual files, it just copies the block data from the drive and writes it to a single img file. What's useful is that it can do this not only for mountable partitions, but for the entire drive if boot blocks are damaged and no partitions are visible.

I believe the sysrescue cd defaults to write-protect mode for non-FAT32 drives, though there should be a way to override this. But writing the img file to FAT32 is fine, even for HFS drives on old macs, because it's just a raw image of the drive. If the image file is in good shape, then it can be copied to OSX and opened/mounted. Then the underlying files should be visible.

If the directory structure of the image file is corrupt, then OSX Disk Utility (and 3rd party software like Disk Warrior or Data Rescue) have features to repair damaged image files. This approach didn't work in my case, though Disk Utility let me burn the image to a CD anyway. The CD was then effectively a clone of my old hard drive, and while it wouldn't mount on the desktop, Data Rescue was able to read it and recover most of the underlying files. [Those files are] based on the dual data/resource forks from the old Apple [hierarical] file system (HFS).

FireWire to SCSI

In 2010 a customer alerted me to the existance of FireWire to SCSI adapters. For example, this company offers both USB to SCSI and FireWire to SCSI devices. THey are I presume one example of other company's products, this is not a recommendation only an example. A Web search may find other company's products, or find used products at Web auctions or personal sales.

Herb Johnson
New Jersey, USA
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Copyright © 2010 Herb Johnson