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Now Available: Yellowstone Universal Disk Controller for Apple II

It’s finally here! After more than four years in development, I’m pleased to announce that BMOW’s Yellowstone Universal Disk Drive Controller for Apple II is available and shipping now. Yellowstone combines the power of an Apple 3.5 Disk Controller Card, a standard 5.25 inch (Disk II) controller card, the Apple Liron disk controller, and more, all in a single card. It supports virtually every type of Apple disk drive ever made, including standard 3.5 inch drives, 5.25 inch drives, smart drives like the Unidisk 3.5 and the BMOW Floppy Emu’s smartport hard disk, and even Macintosh 3.5 inch drives. Yes, pull the internal 3.5 inch drive from an old Mac and use it directly with your Apple II!

Yellowstone Features

  • Add 3.5 inch drive and smartport hard disk support to your Apple IIe or II/II+
  • Provide more disk connectivity options for your Apple IIgs
  • Bring Macintosh 3.5 and naked Apple 3.5 inch drive mechanisms to the Apple II
  • Drop-in replacement for an Apple Liron controller card (with optional DB-19F adapter)
  • Drop-in replacement for a standard 5.25 inch or Disk II controller card
  • Run two drives of different types on twin independent disk connectors
  • Disk II controller emulation mode for tricky copy-protected disks
  • Works with DOS 3.3, ProDOS, GS/OS, and more
  • User-upgradable firmware for future feature enhancements
  • 20-pin ribbon cable connectors or optional 19-pin D-SUB connectors

Yellowstone includes two independent disk drive connectors on the card, and supports drives with rectangular ribbon connectors as well as drives with D-shaped 19-pin DB-19 connectors. The standard Yellowstone card includes two rectangular connectors built-in on-board, and DB-19 female adapters are available separately if needed for use with 19-pin drives. There’s also a Yellowstone Everything Bundle that packs the Yellowstone card with two DB-19 female adapters into a single combined package.

The Yellowstone hardware is powered by an FPGA – a programmable logic device that replicates the behavior of the IWM chip and various support chips normally found on other disk controller cards. This gives Yellowstone unparalleled flexibility and control over every aspect of disk I/O, and the ability to change its behavior through firmware updates.

Limited Availability

If you’re interested in getting a Yellowstone card, don’t wait too long. At the risk of sounding like a late-night infomercial, “supplies won’t last”. The global chip shortage has created major problems for parts availability, and the FPGA chip at the heart of Yellowstone is no longer available anywhere, with estimated factory lead times of more than a year for new parts. If anyone has a lead on some Lattice LCMXO2-1200HC-4TG100 chips that could be delivered before 2023, let me know! The DB-19 female connectors have also become unobtanium. These aren’t manufactured anymore, and the only available sources are dusty new-old-stock from the 1990s. Once the supply of DB-19 females is gone, they’re gone and that’s the end. BMOW has enough Yellowstone hardware in stock to meet a few months’ worth of estimated sales, but beyond that the outlook is uncertain, and it may be 2023 or later before a resupply is possible. Lucky for you, there are plenty of them in stock right now.

Universal Drive Support

Need to attach a disk drive to your Apple II? Yellowstone has got you covered. Yellowstone is compatible with all the disk drives shown in this stack, plus many more. See the instruction manual for complete details.

Final Testing, One Last Moment of Panic

These Yellowstone boards were all tested by the contract manufacturer, using the automated Yellowstone test rig that I’ve described previously. But of course for this first batch, I’m going to spot test some boards at home before I put them in the store. So I grabbed a few from the shipping box, popped one into my Apple IIe, and… it didn’t work. After 10 minutes of troubleshooting I couldn’t figure out what was wrong, and I nearly had a heart attack imagining that the whole lot of Yellowstone boards had some systemic design error. Then I noticed the ribbon cable that I’d grabbed off my desk for testing:

Notice anything strange about this cable, like a giant hole in one of the conductors? Why, Steve, why?! I don’t remember why I originally made this hacked cable, but I curse myself now for leaving it on my desk where I’d accidentally pick it up six months later.

Available Now

If you own an Apple IIe, Apple IIgs, Apple II+, Apple II, or Apple II clone with expansion slots, Yellowstone is the disk controller card you’ve been waiting for! Check out the complete details in the Yellowstone instruction manual, or buy one now at the BMOW Store.

Read 23 comments and join the conversation 

23 Comments so far

  1. Keith - March 18th, 2022 3:38 pm

    No to crow. But following this series of development big entrys, brought me back into the Apple ii hobby scene
    So when the email showed up in my infolder, I had to order just the card right away.

    Thank you Steve for all the hard work. With the twists and hick ups’ along the way. Doing my part to support your efforts. And bringing back my interest into apple ii. As old as the platform has turned into.


  2. Chris Hanson - March 18th, 2022 3:57 pm

    Awesome work! Would the size and power consumption also allow it to work in an Apple III or Apple III+? I know someone wrote a driver for one of the 3.5 cards for SOS, which should also work with your card since it’s compatible.

  3. Steve - March 18th, 2022 4:36 pm

    I don’t know much about the Apple III. Do other standard Apple II disk controllers work with it? I can help with some technical info if somebody wants to work on a driver.

  4. Nick - March 18th, 2022 4:09 pm

    Congrats! I further shared the news on Applefritter and Reddit.

    One quick question, are you including the screw posts with the db19 connectors so they can be mounted in the back of say, a IIe? They aren’t shown in the pics or mentioned in the description.

  5. Steve - March 18th, 2022 4:38 pm

    The DB19 female does include tiny removable end posts. I found them very difficult to unscrew, and had to try many different tools before I hit one that worked. Here’s a close-up photo of the DB-19F with one post unscrewed:

  6. Patrick+Kloepfer - March 18th, 2022 4:27 pm

    Everyone, I was lucky enough (like winning the lottery!) to test the Yellowstone pre-production, and in short, WOW! I am so glad to see it out of productions. Steve has done a hell of job on this. To independently verify what Steve has already said, this thing works with everything! Having both 20 pin ribbon connectors as well as DB-19 is a godsend. You can plug in anything from a Disk ][ to a Duodisk to a 3.5 drive, not to mention the Floppy EMU in any mode. As for compatibility, I tested the Yellowstone with both enhanced and unenhanced //es, a //GS and even an Apple II clone, along with a //E Transwarp and a FastChip. For operating systems, I had it running DOS 3.3, ProDOS 2.03, 1.x (1.8 I think), ProDOS FX, Apple Pascal and CP/M. For Apple Pascal fans, I was able to run 1.3 off 800K disks booted on the Yellowstone. Steve, congrats on this great release!

  7. Chris Hanson - March 18th, 2022 4:46 pm

    It looks like there’s a driver for the Liron card here:

  8. Chris Hanson - March 18th, 2022 4:46 pm

    (Oops, forgot to edit that one last time.)

    It looks like there’s an Apple III SOS driver for the Liron card here:

  9. Darrick - March 18th, 2022 5:12 pm

    You probably hacked the cable for this post.

  10. Steve - March 19th, 2022 7:01 am

    The hacked cable is newer than that. I think it was part of my testing for this issue:

  11. Leslie+Ayling - March 19th, 2022 4:35 am

    Great work Steve, and the beta testers.
    Been very much looking forward to this one!

    Order already in.


  12. Leeland+Heins - March 20th, 2022 3:57 pm

    I already ordered two…

  13. Leeland+Heins - March 21st, 2022 9:27 pm

    I got a ship notice for my two cards today!

  14. Steve - March 22nd, 2022 7:03 am

    Shipping is backlogged for several days, unfortunately. In the space of a weekend, I received as many orders as I normally do in two months! I’m working with my assistant to get these packed and shipped as quickly as we can, but it’s probably going to take about a week. Sorry for the delay.

  15. Leeland+Heins - March 22nd, 2022 4:47 pm

    Should be well worth the wait. In anticipation of this I ordered two more FloppyEmus a month or two ago. It will be fun to use them with the Yellowstone. I have a LIRON card (and a couple of Laser UDCs, etc), but the Yellowstone is much cooler.

  16. Nick - March 23rd, 2022 9:00 am

    My shipment not only came a day earlier than USPS had stated originally, my mail carrier came around 4 hours earlier. So I was able to quick install the Yellowstone and give it a very quick try during my lunch.

    Everything worked as expected. The only thing is the head knocking at boot up is triggering my OCD. It knocks much faster than a standard drive controller does. Is there anyway possible to tweak the firmware so that it knocks at (or very near to) the “standard” rate? A lifetime of hearing that knock has been ingrained in my brain.

    And lastly, I’m trying to determine if I really need both db19 headers connected. Will the FE daisy chainer work with this? So for example I set the FE to 5.25, connect it to J1 using the chainer, then connect an Apple 5.25″ drive behind it? That should be the same as what the manual shows as being valid if the FE was an Apple 5.25″ drive as well. I’ve only used it with my IIgs, just want to make sure it’s safe to use here as well.

  17. Steve - March 23rd, 2022 10:59 am

    The knocking sound is a side-effect of the code that does track stepping. If you’re only using 5.25 inch drives, you can put the Yellowstone card in Disk II mode, which will also make a different knocking sound. Regardless of the sounds, the 5.25 inch disk functionality is the same. Yes you could use the Daisy Chainer that way, then you wouldn’t need any DB-19F adapters.

  18. Leeland+Heins - March 25th, 2022 9:34 am

    I received my two Yellowstone cards in the mail yesterday. I haven’t had a chance to try them out yet.

  19. Ricshaw - April 4th, 2022 3:12 pm

    The Yellowstone card arrived yesterday afternoon (OZ time) and I re-read the user manual one more time. Installed said card into slot 6 of my //e, set the start up from Apple II disk mode, to Smartport and low and behold your Smart0 image loaded first time. I never thought anything else though. That was using my Emu “C”. Now to add the Emu “B”, I’m assuming that I add the Daisy Changer device with the Emu “C” as the first device, then add the Emu “B” after that. A question though, do I have to first connect the Emu “B” to the //e to set it up as a Smartport device, then set up using the Daisy Chain unit?
    By the way delivery to OZ was fine using the new method.
    Best Regards,

  20. Steve - April 4th, 2022 7:48 pm

    You won’t be able to daisy chain two Floppy Emus where the second one is emulating a Smartport drive – this is a limitation of the Daisy Chainer, where the attachment of downstream Smartport or Unidisk 3.5 inch drives is not supported. (See the compatibility info at But you shouldn’t need to do this anyway, since the first Floppy Emu can emulate up to four Smrtport drives simultaneously all by itself. Just add the files smart0.po, smart1.po, smart2.po, and smart3.po to your SD card, or one of other supported filename formats. See the Floppy Emu instruction manual for details.

  21. Rick - April 6th, 2022 4:19 pm

    Tested my Yellowstone with external 800K 3.5 drive, and I am happy to report it works! Great Job Steve.

  22. Rick - April 6th, 2022 4:21 pm

    …meant to say it works in my Apple ///.

  23. Rick - April 6th, 2022 4:22 pm

    …meant to say it worked in my Apple ///.

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