A Little History

My Maxed Out Quadra 950

My first experience with a Quadra 950 was back when they were new. Mike Bean, then president of the Arizona Macintosh User’s Group, had one.

It was big. It was loud. It was fast… and it was beige. I loved it!

Mike also had a Workgroup Server 95, the Unix-based file-server version of the 950, and he let me use it for an experiment involving an FTP server and a brand-new T1 based Internet connection. It wasn’t long before we were serving roughly 8% of NSFNET’s traffic. Yes, 8 percent. NSFNET was essentially the backbone of what would become the Internet, so this was a rather ridiculous amount of traffic for a lone Macintosh sitting in Arizona.

Seemingly, the only thing holding us back was the 32 MB of RAM in the server.

Eventually, we outgrew the Workgroup Server 95 and moved the load to a Sun SPARCstation 20. Still, all these years later, I wondered what would happen if I could fill all 16 SIMM sockets in a that machine with 16 MB SIMMs, the largest size the machine could use.

So I decided to find out.

The Search

A quick surf of the usual places turned up several sellers with 16 MB SIMMs in stock. The price was… not terrible. Not wonderful, either. It got me thinking.

I searched for “16 MB SIMM open source hardware” and discovered that Bits und Bolts had designed boards that could be populated with the necessary memory chips and configured to work with either Fast Page Mode (FPM) RAM, as used by Macs, or Extended Data Out (EDO) RAM, as used by PCs. A little switch on the board selects between the two.

Cool!  Those could come in handy for repairing other vintage machines too. I’m in!

I ordered a pile of bare boards from PCBWay, switches from AliExpress, voltage regulators and capacitors from Mouser, and spent far too much time looking for a suitable donor DIMM on eBay. I found one. It was a monster: a double sided, double height 256 MB parity EDO DIMM.

The fact that it supported parity was actually a bonus. It meant the DIMM had eight extra memory chips on it. And when you’re making 16 MB SIMMs with two chips each, more is better.

Once it arrived, I spent some quality time with a hot-air rework station and stripped it down to its individual chips. Into the recycling bin went the carcass of the DIMM, leaving me with a nice pile of memory chips.

A short time later, the boards and the rest of the components arrived.

Time to build

Making Memories

I soldered the memory chips and other components onto the new SIMM boards, cleaned everything up, inspected the solder joints, fixed a few that I had missed, and started testing the SIMMs, four at a time.  It took a while.

After fixing “a few” more questionable solder joints, I finally had a complete set of maxed-out SIMMs for my Quadra 950.

If only I’d had that much RAM when I was running the Workgroup Server.

I’d have… Well, I’d probably have been better off buying Apple stock.

The Memory Test From Hell

I populated the 950 with a full load of brand-new 16 MB SIMMs and turned it on.

Then I waited. And I waited. And waited some more…

When Apple designed the Quadra 950’s boot process, it made sense to perform a quick memory test before loading the operating system. At the time, 8 MB of RAM was a respectable amount, and 32 MB was getting into the realm of the absurd.

But 256 MB? The memory test took ages. I had to do something about that. Fortunately, I like repairing old Macs.

Recently, I’d built a couple of Mac IIci Reloaded boards designed by max1zzz. One of the tricks I use when building those is a ROM SIMM. I initially solder in only the minimum number of components necessary to get the board running. That makes troubleshooting much easier. Fewer components means fewer places to look when something doesn’t work. I usually install the SIMM sockets and SCSI connectors last.

The ROM SIMM socket, however, goes in early. A ROM SIMM can contain a bootable operating system along with diagnostic utilities, making it a very useful tool when testing a mostly assembled logic board.

It turned out to be an even better tool for my Quadra 950.

There are several ROM images available for the 950. Some contain a bootable operating system, while others even have modifications that allow you to bypass the memory test. I downloaded one that bypassed the memory test, flashed it to my ROM SIMM, installed it, and…

Phew. The 950 booted without spending an eternity counting its memory. That problem was solved.

On to Mac OS

System 7, unsurprisingly, loves having a ridiculous amount of RAM. I happily posted a screenshot of the machine showing its full 256 MB on the Low End Mac Facebook page and received the inevitable question: “Why?”

Now you know why. It was a fun thing to do.But I wasn’t finished.

A/UX

Next up was A/UX, Apple’s Unix operating system and the software behind the venerable Workgroup Server 95.

I loaded an A/UX image onto my BlueSCSI SD card, booted the version of Mac OS that A/UX requires, waited for it to start the Unix environment and…

Nope. 256 MB was simply too much for A/UX.

Fine.

I wasn’t going to re-solve the problem I had already solved 30 years ago with an absurd amount of RAM anyway.

I pulled half the SIMMs.

128 MB – Surely that would work.

Nope. Still too much.

Fine.

64 MB – That worked.

But 64 MB is a positively boring amount of RAM when you have sixteen memory sockets sitting there on the logic board, all of them practically begging to be filled.

It seems Apple designed A/UX around the hardware specifications that actually existed when it was released and didn’t leave much room for expansion beyond them.

Would doubling the amount of RAM we had in the original Workgroup Server 95 have helped? Probably. Would even more have been cool? Absolutely. Was Apple interested in maximizing RAM when developing A/UX? Apparently not.

Was It Worth It?

Is it worth putting 256 MB of RAM into an ancient Quadra 950?

Short Answer: No.

It won’t make games run faster. Photoshop on a machine like this is of questionable usefulness, and there are very few applications from the era that can actually take advantage of that much memory in a meaningful way today.

But that’s not really the point. Sometimes you just have to do something you’ve always wanted to do simply because you can. Thirty years ago, I wondered what would happen if I could fill one of these machines with memory.

Now I know. 256 MB! And A/UX only can handle 64 MB… In the end, it’s another item checked off my bucket list.

If I had a bucket list.