High Treason's Museum

Systems

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High Treason's Museum - Systems - Krystal \ Quick Overview

Overview

Krystal as of September 2022

Sometimes people build an old PC for maximum performance, others insist on accuracy and some do it purely for fun. This computer does a little of each. Named for the character from Dinosaur Planet (The Nintendo 64 game, not the Game Cube one), the machine is nowhere near as pretty but is certainly rather special. For some time, the 486DX-50 was the fastest x86 processor available and had a considerable lead over everything else. Unfortunately its time clashed with that of VESA Local Bus, whose peripheral cards didn't much like operating at 50MHz. To negate the issue, you could introduce Wait States, but this would degrade performance significantly, essentially wasting any gain you would have gotten from the CPU. It is likely no coincidence that most DX-50 CPUs seem to show up in EISA systems, a bus with its own clock source. Hard drive interfaces in particular will dislike running on 50MHz VLB and may well end up corrupting data, or outright crashing the system, if they even show up at all. All this and yet somehow, on this system, we got lucky and made it work.

The motherboard is worthy of note as it is actually harming performance, in a way. The motherboard actually performs at a level I'd consider rather average, but for 1992, when the 486 platform was a whole lot less mature. Its CPU support is limited to 5 Volt chips on Socket 2, which is fine for us here. There is no 40MHz support, a speed used as a compromise by AMD, Cyrix and UMC later on. Krystal's motherboard still uses SIMM RAM, its chipset (UMC481/482) predates the introduction VLB so can't take much advantage of it, nor is it able to do fancy interleaving with memory, or access the cache all too quickly. This is what I wanted, however, as whilst a later board would easily flatten it, this one provides the authentic experience of the DX-50 - and I know for certain this CPU has been with it since new - whereas people had moved onto the DX2-66 by the time the later, faster boards came around. If I wanted speed that badly, I'd use a modern computer. Still, in any case, Krystal would have been considered High End in 1992.

The VGA card is a Chips & Technologies F64300 which claims to be for evaluation use only, so was likely a review board sent out to magazines or system designers. This card is itself novel for the fact it will work on a 50MHz VLB system (no guarantees they all will) and for having cache memory onboard, a mere 512KiB. This does little to nothing in the real world, but it was a novel concept at least. Otherwise it's a 2MiB GUI Accelerator which performs pretty much the same as a TSeng ET4000/W32P, produces good image quality and seems to be quite compatible with almost all software, maybe more so than the TSeng cards, which are prone to a few small issues.

Attached to the VGA card is a Digital Equipment Corp. Full Video MPEG Decoder card. This card is a little bit of an anomaly. I have never seen another one in the wild, although they must exist somewhere. It claims to be a VCD Decoder that will work as far back as a 386SX at 25MHz. I'm skeptical about its operation without an x87 present, but in any case, the card does not perform as advertised in my DX-50. The ISA bus shouldn't be a problem for it, as this is running within spec and the manual even recommends turning it up higher - odd, as if it took the raw MPEG stream, it shouldn't need much bandwidth. In general, streams of VCD quality will fail to play properly, causing an effect that looks like the DMA is choking when, in fact, it's the card stalling hard. You have to play files with lower bit rates, lower quality and lower frame rates. I was puzzled when none of my files would play, only to put the demo CD in and have it come right up - all of the files are only 12fps at much lower quality than actual VCD streams. Files from officially pressed VCDs will not play properly, if at all on this card. One nice thing it has going for it is that whilst it is under license from RealMagic (who must have hated having their name on it), it uses the digital Feature Connector instead of that dumb analog cable. This results in no image degradation as the card gets a digital copy of the frame buffer directly, but has the down-side of limiting you to only 256 Color modes on your VGA card - of course the MPEG playback is composited in at full color.

At the time of writing, the CD-ROM drive was the only SCSI drive I had spare, but is a 2000s burner. It is on the to-do list to replace it with a more appropriate SCSI CD-ROM drive, likely from the mid-1990s. If you have seen the system's video on YouTube, you will have seen it with the Mitsumi drive, but this was moved to Lisa, as it seemed more fitting there.

The 486DX-50's reign wasn't entirely smooth and it was also short. Intel would never again release a 486 processor for a 50MHz bus, but this would not, however, be the final non-clock-multiplied CPU from Intel running at a high bus speed. That honor would soon befall the Pentium, which was initially going to be available in a 50MHz version.

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High Treason's Museum - Systems - Krystal / Specs

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System Performance

As you can clearly see in the cramped set of results here, the DX-50 was a very fast CPU for its time. The later DX2-50, on the other hand, I would consider a ripoff and it seems nobody but dumb OEMs ever used them. The DX2-66 was rightly a popular chip, but I feel it would have been largely ignored by anyone who owned a working DX-50, as the performance isn't too far away. All CPUs were tested in Krystal here, rather than other systems.

We can test with another system, however. Hooker is a more mature 486 system using the UMC498 chipset. This is shown in red, using the uncommonly quick UMC U5SD-40 CPU, a 486SX type processor at 40MHz. Krystal does not support 40MHz operation regardless of jumper settings, so was tested with a 33MHz version of this same CPU, shown in blue. It should be self-evident just how much faster later 486 motherboards were.

This only becomes more apparent if we focus on SpeedSys, as the chart is less cluttered here. Pretty much no contest.

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Pictures

Krystal's cover removed. 486 motherboards were still fairly large when the UM486V was designed, but just small enough to be Baby AT. Our chassis is thankfully quite well designed, so it isn't too difficult to work in there.

The rear of the machine as of September 2022, with the MPEG decoder and its terminator installed on the VGA card. It will work without this dingleberry present. Otherwise you can see that even this late on, very few things were built into the motherboard and we have to use up loads of slots.

The VGA card. This chipset is uncommon, but for most uses it works about as well as several other cards, so if you just want things to run, don't worry about hunting one down. That said, it does work quite well and is undeterred by the 50MHz bus clock.

SCSI was always a gamble in a 50MHz VLB system, which is why I just had to use it in here. This DTC card has jumpers especially for such cases and the hard drives were slow enough that you'd probably never notice a hit in performance.

Another shot of the motherboard, from before it was installed in the chassis. Note the blue Socket 2. This processor was installed in this board when it was new and has been there ever since, aside from my brief tests with other CPUs.

The CPU socket actually has writing beneath the CPU, which advertises OverDrive compatibility. I do not believe this board is fully compatible with the Pentium OverDrive CPUs, despite the intention, because of Intel fiddling with the specification before the CPU released, three years after the board.

An initially confusing but undeniably cool pivot in the chassis allows better access to the motherboard without having to remove it. This is actually necessary to perform if you do want to remove it, however, so you'd better figure out the hinge and its little catch mechanism if you have such a chassis.

MPEG Decoders are novel devices, but this one is particularly fun as the claims on its box are rather dubious.

And the box in question. DEC made some really strange things late on. When this card was produced, there was a lot of turmoil inside the company, which had just posted a loss of nearly $200,000,000 and had seen its stocks plummet by around 20%. No doubt this peripheral didn't help their situation. Very sad.

Sound is provided by the Logitech SoundMan 16. This is just a Media Vision Pro Audio Spectrum 16 with different branding. It also offers no CD interface, has different audio connectors and no internal speaker output. Still a very good card.

The dedicated I/O cards for Serial and Parallel. This maybe isn't the most 'appropriate' solution, but the cards weren't doing anything otherwise and the slots were free. What really matters is that we have the required interfaces there. If a spare slot was needed, it would be trivial to replace these with a combo card.

You can click the above pictures to see full size versions in a new window

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System Achievements

Krystal holds a few records:

• Only 'Socket 2' machine in the collection

• Second fastest single clocked 486 processor in the collection

Ooh-laa!!!

Videos Available

Krystal's main overview video, which goes into more detail than this article ever realistically could and has a focus on testing performance. At the time of writing, this machine is planned appear again some time.

Video for Windows v1.1