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Amiga Bridgeboard: The PC compatibility option

A photo of someone’s newly acquired Amiga 2000 turned up on a vintage computing forum recently. It was sporting two 3.5″ drives, but also had a Chinon 5.25″ drive in its lower bay. Someone asked what the 5.25-inch drive was for. I responded it’s a good sign the system has an Amiga Bridgeboard in it. The Bridgeboard turns a big-box Amiga like a 2000 into an odd hybrid Amiga-PC clone.

First released in 1987, the Amiga Bridgeboard consisted of most of an IBM PC clone on a single full-length card. It had its own ISA bus, but it was also able to access some Amiga functionality, not just to provide IO but also to provide ways to share data between the two systems.

Why Commodore released a PC option for the Amiga

Amiga Bridgeboard

The Amiga Bridgeboard added an 8088, 80286, or 80386SX-based PC to a big-box Amiga via a plug-in card like this.

The knock on the Amiga from the beginning was that it wasn’t compatible with anything else. The Bridgeboard provided a way to rectify that, by optionally making the Amiga able to run standard IBM PC software. Making it an option kept the cost of the Amiga lower for people who didn’t want or need IBM PC compatibility, which was important. The Bridgeboard initially sold for around $500. IBM compatibility wasn’t as cheap to implement as some people think they remember. Commodore theoretically had the ability to design its own PC chipset, but they used an off-the-shelf chipset from Faraday.

The Amiga Bridgeboard initially came in two flavors, the 2088 and 2286. The 2088 sported a 4.77 MHz 8088 CPU, matching the original IBM PC and XT. The 2286 sported an 8 MHz 80286 CPU, which matched the IBM PC/AT. Commodore followed up in 1992 with the 2386sx, which had a more useful 16 MHz 386sx CPU, but came at a higher cost. A third party also offered a 386sx Bridgeboard it called the Vortex Golden Gate. This was a bit faster than Commodore’s model, and eventually it also came in a Cyrix 486SLC flavor. Vortex offered upgrades for Commodore’s 386SX Bridgeboard to a 486SLC as well.

Commodore’s Bridgeboards included the board, which plugged into a dual ISA/Zorro slot inside an Amiga 2000, 3000, or 4000, along with a 360K or 1.2MB 5.25-inch floppy drive, instruction manuals, MS-DOS, and the software required for the Amiga side, which Commodore named Janus. Janus was a Roman god with two faces, one that looked to the past and one to the future.

Using the Amiga Bridgeboard

I owned both the A2088 and A2286 versions of the Bridgeboard. My 2088 was extremely fiddly. Maybe they weren’t all like that, but mine certainly wasn’t all that reliable, even by the standards of the late 80s and early 90s when everything tended to be flakier than we expect now. I had to take it out and reseat all the chips in it more than once. I picked up a 2286 on closeout in 1992 or 1993, and it was a lot less fussy.

Getting a Bridgeboard to work was difficult for someone used to the Amiga, which essentially had plug and play-like functionality from the get go. If you had to set jumpers or flip switches at all, most cards only had one option you had to set. They could figure out pretty much everything else. That kind of ruined the PC experience.

The other problem with the Bridgeboard was some of the IRQs and I/O addresses were in use. And I’m not sure anymore if they were documented clearly and I just missed them, or if Commodore missed those details in the documentation.

If you just used the Bridgeboard with no add-ons, it wasn’t too bad. You just plugged it in, loaded some software on the Amiga side so the Amiga could share its keyboard and mouse with the PC and let it use an Amiga window for its display, set up a file on your Amiga hard drive to emulate a PC hard drive, then loaded DOS.

And being able to run text-mode DOS programs in an Amiga window and copy and paste between them and the Amiga was pretty slick. But the Amiga could only emulate CGA and MDA, and by the time the Bridgeboards hit the market, VGA was the standard. Once you plugged in a VGA card, things got clunkier. You had two computers sharing a keyboard and mouse, but both of them needed their own display.

Who bothered with the Amiga Bridgeboard?

I got a Bridgeboard because I thought having multiple computers in a single box was cool. Then again, I also had a Commodore 128 and thought it was pretty cool.

But it wasn’t super practical. I found an ad from mid-1989, advertising a 2286 Bridgeboard at $1,079. But some brand-name 286s were selling bare for right around $1,000 at that time. In the back pages of the August 14, 1989 issue of Infoworld, I found a company selling no-name 286 clones for $700. The only thing you really gained by using a Bridgeboard instead of getting a PC was being able to share hard drive space between the two machines. But this came at a speed penalty.

If you were an Amiga owner and needed to be able to run PC software, it was more practical to get a PC and give your Amiga a roommate, unless you really didn’t have room for a second PC.

If Bridgeboards seem rare today, that’s why. I didn’t pay anywhere near retail for mine, but that’s probably why I got them cheap. Commodore was blowing them out due to lack of demand.

In practice, the Bridgeboard experience wasn’t all that different from the add-on boards for PCs from the early/mid 90s that promised to turn your PC into a game console. They worked, but cost as much as the console and tied up your computer, so why not just buy the console? That’s what most people did.

But I do think the availability of the Bridgeboard helped sell Amiga 2000s. People liked having the option, even if they never followed through on actually buying it.

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