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A Pentium 3 with... RDRAM? The Dell Precison 220

09 Jun 2023 - faintshadows

Coming up to a year ago now, I visited a friend who needed to thin out their computer collection. I had a few friends visiting from out of town as well, so we made a whole day out of it. I came back with quite a few machines, that HP Jornada 680 being one of them. Another one I got was a Dell Precsion that I didn't think much of, it was mostly to have a Pentium 3 system while my main one, another Precision, was back home in Florida. It was intened to be temporary, but there's something different about this, and I didn't think this was a legal combination.

It has RDRAM.

I always thought RDRAM in PCs was relegated to the original Pentium 4 chips before Intel backpedaled on that and went to DDR. Pentium 3's only got SDRAM. Yet here it is, a dual Slot 1 board sporting the cursed RAM standard. Outside of that, it's a normal PC of the era. AGP 4x, PCI, USB 1.1, IDE, etc. An unremarkable machine. You wouldn't know just looking at it.

I only found out about this RDRAM business when I was getting memory test errors on POST, and opened it up to see only two slots, and shiny metal heatsinks. The mark of the beast.

Testing the memory with Memtest86+, almost right away I get an error at 434.5MB of the 512MB total, so the 2nd 256MB RIMM is dead. I have more RDRAM that I got years and years ago, but never had a RDRAM system to test it in. This marks my first, so I can at least check that the rest of my RIMMs work, and finally toss out the ones that don't.

The board in this PC sports the Intel 820 Chipset¹, and only supported RDRAM natively. Use of SDRAM required extra circuitry on the board to translate it. And even then, you were stuck to PC100 speeds, not even PC133, which the 810E supported and came out about the same time.

Now, this is a Dell Precision after all, their workstation line. So utilizing the newest chipset and memory technologies is no surprise. I still find it odd, though. There isn't anything super high performance about this, it's a single 733MHz standard Pentium 3, no Xeon, no SCSI, PCI-X, none of that. They even cost-reduced out the ISA slot! Maybe this was just the bottom of the line that also included the 820 chipset, a weird in-between.

One of the big selling features of RDRAM was its performance, it claimed to have really high throughput. Now, I don't know how exactly to measure effective RAM speeds in a system, nor do I have my other Precision here to test. But the napkin math says PC100 is effectively 800MB/s. Memtest86+ says the RDRAM in this system is at… 348MB/s. So much for that.

It's possible the speed test from Memtest is not really reliable for RDRAM, but given what I've read about RDRAM, the shortened bus width compared to even SDRAM (16bit vs 64bit) probably isn't helping it here. If we learned anything from the RTX 4060 (hereby dating this post instantly), slicing down the bus width never goes well.

Going into the BIOS states the channel speed is 400MHz, making this PC800 RDRAM, which theoretically would be double PC100's 800MB/s with 1600MB/s, theoretically.

Given I have to replace the bad RIMM anyways, we'll explore the other modules I have and see if I can't do any better than that. At a first glance, I can't. Of the four RIMMs I have, two are 128MB, and two are 64MB. The ones I took out were 256MB. Unlike SDRAM, I can't really mix and match sizes, everything has to be done in pairs, so the best I can get is 256MB. Memtest+ also reports this other set of RAM as 348MB/s, which makes me think it's bottlenecked somehow. Which I think is a shame, given the 733MHz P3, I think it deserves better.

Both the 64MB and 128MB pairs passed Memtest with no issues. Unsure if its worthy of note, but for completion's sake, the 64MB set clocked in at 329MB/s according to Memtest+. None of these sets are ECC, but according to Dell's documentation, it doesn't mention any support of ECC, though the chipset does support it. ECC isn't any useful to me, so I won't pursue getting any.

That's about all I have this time. I have some things I want to do with this Precison, I recently got the InfoMagic Linux Developer's Resource, Summer 1999 edition. A quick glance shows it's not archived on the Internet Archive, and I'll try to get that up there soon. But what's on there? Stay tuned to find out ;)

~faint

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