I just had a re-read of this post. I love the board and the case. I've always wanted an EISA 486 with VLB video but have enough retro computers at the moment. This hobby takes a lot of patience (7 years in your case!) That is a very attrative case; it will look good when oriented in both the horizontal and vertical positions and is nice and white with matching drives. A nice case is essential to any fine combination of hardware.
An intel dx4 at 150MHz would be pretty sweet though...
Has anyone tried this yet? That would have made for a great addition to the UMBC, or even at 133 MHz (2x66MHz). I think I'll add these to my "When I'm Bored" list of things to do.
It's unfortunate that my board does not have a removable oscillator to adjust the bus speed. I would have liked to see what would happen with a 45MHz bus.
A solder pump or rework station will make it removable. It should just be a 2-pronged oscillator chip at 14.X MHz or something like that. Then you can put in a socket in its place and have removable oscillators. Actually, this is a great idea in general for customising the bus speed; using discrete removable crystal oscillators to adjust the clock. I don't think this will make my "When I'm Bored" list though since I've been happy with 2x66 MHz operation lately.
So its seems that both UMC and SiS chipsets can be clocked to 66 MHz, even the ancient SiS chips. Does your northbridge get hot? If you place a temerpature element on the northbridge, how hot does it get? A simple test would be to place a SMD NTC thermistor (i.e. 10K) on top of the northbridge and read the resistance to determine temperature.
You mentioned that one of your AMD ADZ chips would not stably operate at 160 MHz. Was it of revision 0494 or 04F4? I find 04F4's to work much better for overclocking.
For your SpeedSys image with "Final results with Cyrix 5x86 120. BTB_EN and FP_FAST". Try setting LSSER = 0 and/or MEM_BYP = 1. LSSER set to 0 has just as much impact as BTB set at 1. Then try re-running GTA1 and SpeedSys. I have now finished my Cyrix 5x86 Special Feature Comparison and charts, but have't had the mood to do the write-up yet.
I'm actually not sure about LVD drives. I assume they might work though, since SCSI is usually pretty good about being backward compatible.
There should be a jumper on the harddrive to force it into Single-ended (SE) mode, at least the Seagate LVD drives have this jumper.
I figure GTA1 must be ALU intensive, because if it were heavily FPU dependant, it would likely run much better on the Cyrix 5x86 than on the AMD chip.
From my tests, I've noticed that DOOM seems to be more ALU intensive, while QUAKE seems much more FPU intensive. GTA1 could be more like DOOM.
Perhaps if I can boost the voltage on my VRM, I could have a shot at 2x66.
If you can, shoot for 3.85V.
Would a 5x86-120 do 66x2?
I'm not sure I understand the question. A Cyrix 5x86-120 should operate with a clock multiplier set at 2X and a FSB of 66 MHz. I find 3.85V to be the sweet spot for Vcore. Refer to the post, So you want a Cyrix 5x86-133 and The World's Fastest 486 for more details on this setup.
So you want a Cyrix 5x86-133?
The World's Fastest 486