The ESDI-Emu: ESDI Disk Emulation

For the last few years I've volunteered at the System Source Computer Museum. I've done a couple of projects for them, some of which I've described in this blog. But this has also exposed me to the world of vintage personal computers. Hobbyists spent incredible amounts of time collecting and restoring computers from the dawn of the PC era.

One of the challenges in the "vintage" computer world is finding replacement parts. Maybe you need to fix a vintage keyboard whose foam components have turned to goo. Or you have a 1980s era PC that requires disks with the ST-506 interface (often called "MFM" disks for the recording format). I have a VAXstation 3100 that requires narrow-bus SCSI disks no larger than 8 GB. An entire cottage industry has evolved to satisfy these needs.

Skipping ahead 9 months...

When I last wrote in this blog last December I'd just completed Lesson 2 of FEDEVEL's "Advanced PCB Layout" course. By mid January I'd finished all the videos and then went back over several of the lessons I thought were most relevant. Robert Feranec is a good instructor with clear mastery of the topic.

As good as that class was, I still felt I needed a bit broader coverage. I've been doing digital design as a hobby for over 20 years, but I knew I was making some decisions based on guesses rather than good data. I decided to invest in FEDEVEL's "Advanced Digital Hardware Design" course, taught by Philip Salmony who also makes the "Phil's Lab" YouTube videos. The "Zett Brett" design he discusses in the video has many parallels with my latest project. I'd already completed almost all of my design by the time I started this course, but it gave me added confidence in many of my decisions.

FEDEVEL Advanced PCB Layout: Post Lesson 2 notes

I finished Lesson 2 of FEDEVEL Academy's Advanced PCB Layout course yesterday. As I expected, there ratio of review to new material (for me) is shifting toward the new stuff. There were a couple of confusing points, like the the instructor's strong recommendation to use a separate via for each power and ground connection on a BGA while watching him demonstrate routing two such adjacent balls to a shared via. Some of the recommendations  offered were things that I had read elsewhere, but it was nice to have it explained from another person's viewpoint.

And there were a couple of "Wait, what?" moments. 😯

Taking FEDEVEL's Advanced PCB Layout Course

As part of a hobby project I'm designing a PCB that will include a Xilinx Zynq-7000 System-on-Chip and a DDR3L SDRAM. Both of these come in ball-grid array (BGA) packages with balls on a 0.8mm grid. This is my first attempt at a PCB using BGAs, but more critically, it's my first attempt with high-speed DRAMs.

I'm fairly confident, but at the same time I'm a little bit intimidated.

A look at a vintage PC's disk storage subsystem

I've been doing a lot of work recently with vintage PC disk storage subsystems. I'm hoping to present a talk on this topic at the VCF East event in April 2026. Here's a preview of some of the material I'm planning to present.

 As always, comments and questions are encouraged. 

My current museum project

Here's what I'm currently working on restoring for the System Source Computer Museum:

Yes, this is an IBM System/360 Model 20 from the mid 1960s.

This machine's journey started with some friends drinking in a pub in the UK while browsing eBay. They came upon an ad for some computer equipment in a building due for renovation in Nuremberg, Germany, and decided to put in a bid. If this already sounds like a recipe for disaster, well, I'd agree. 

I really can't do justice to the effort they put into the recovery. It's best if you read it in their own words here: https://www.ibm360.co.uk/

To make a long story short (and you really should go read their blog), it's on long-term loan to our museum for restoration.

Computeriter Emulator wrap-up

Okay, so it's been 5 months since I updated this blog. I have some catching up to do!

Spoiler alert: I did get everything working in time for VCF West. Here's a pic of the CDC-160A system on display in sunny California:

 

What did it take to get it done? I pretty much lived and breathed for this project from mid April through early August. But let me catch you up on what you missed.