VLB IO cards at >33MHZ bus speed are quite a mess. As far as I remember, most onboard IO solutions were providing stable operation if the board itselb supported 40 or even 50 MHz.

Back in the days I remember having absolute zero issues with my Cyrix 486 DX/2-80 at the time (I don't remember the board, but IDE/serial/lpt... all but sound and graphics were onboard), even at 50MHz (DX/2-100 ftw...)!
But all my friends have been struggling a LOT with 40MHz bus and beyond. I had the (inadvertedly happy, as if I would have known about these thing back then) benefit of having to use just one VLB slot for graphics. And that (in hindsight very sorry thing of a dead slow) Cirrus Logic-VLB card even did take 50MHz like a charm. Most of my friends systems worked well beyond 33MHz, when using VLB-graphics and ISA IO-cards. But somehow, even with IO being the only VLB-card inserted, IO cards always seemed to my the firstmost point of failure when overclocking the bus.

I think you need to pay attention to the IDE controller on the card, not the floppy / multi-io controllers.

I think Promise, CMD, W83759AF, SIS 601 and ADI2 based controllers generate their own strobe signals for the IDE cable, which gives them better reliability when talking to PATA devices as the VLB signal speed changes.

QDI, UMC and cards that use jumpers to set the IDE speed often generate their strobes for the IDE cable from the VLB signal, and this can make things more sensitive to any imperfections when the VLB speed increases.

If you are having trouble with a card that has speed jumpers, you can try setting a lower speed on the jumpers to see if that improves things.

Lucky you.

I never had joy with vlb even at 33, back then and now.

Not that I have a selection of cards or a means to get any.

Just running everything straight isa in the DX4.

With some cards the IDE timing goes out of spec at higher bus speeds. So if you are using a very old/slow HDD, or a finicky IDE-to-whatever adaptor, it might be worth trying a newer (ultra ATA 33 or better) HDD.

If you're using a VLB video card, you can try swapping that, as sometimes cards don't agree with each other. I had a low-end Trident of some kind (9320?) that would always cause problems. My current combo of Trident 9440 and EIDE2300-Plus works fine at 40MHz, with a Quantum Fireball. Though I have never tried a UMC CPU.

douglar wrote on 2026-02-04, 13:57:

I think you need to pay attention to the IDE controller on the card, not the floppy / multi-io controllers. […]
Show full quote

I think you need to pay attention to the IDE controller on the card, not the floppy / multi-io controllers.

I think Promise, CMD, W83759AF, SIS 601 and ADI2 based controllers generate their own strobe signals for the IDE cable, which gives them better reliability when talking to PATA devices as the VLB signal speed changes.

QDI, UMC and cards that use jumpers to set the IDE speed often generate their strobes for the IDE cable from the VLB signal, and this can make things more sensitive to any imperfections when the VLB speed increases.

If you are having trouble with a card that has speed jumpers, you can try setting a lower speed on the jumpers to see if that improves things.

Thank you, this is news to me. I have five VLB IO cards and they are all UMC, Goldstar or Winbond - various different ICs, but they all have speed setting jumpers and none of them seem to work reliably at 40MHz even at the slowest setting and extra wait states. I don't find it a huge problem in DOS, to be fair, to use an ISA IO card, but I guess it could have been an issue if I wanted to run Win32 on a 486.

I love my UMC U5S-40 setup, it is amazingly compatible for DOS and runs speed sensitive things like Ultima 7 and Theme Park super well. Not being able to fully upgrade it is making my inner OCD go crazy 🤣

appiah4 wrote on 2026-02-04, 12:10:

Back in the days I used to own a 486 DX33 and upgraded to a DX4-100 and never had an issue with my VLB IO. The 40MHz FSB is really driving me crazy..

I thought both DX 33 and DX4 100 ran on 33MHz FSB.. so it makes sense that nothing breaks between the two. 40 MHz FSB is for a DX2 80.. is that what you're going after?

For the record I also never found a VLB card that worked reliably above 33MHZ FSB... Not IO not VGA...

wbahnassi wrote on 2026-02-05, 07:04:

appiah4 wrote on 2026-02-04, 12:10:

Back in the days I used to own a 486 DX33 and upgraded to a DX4-100 and never had an issue with my VLB IO. The 40MHz FSB is really driving me crazy..

I thought both DX 33 and DX4 100 ran on 33MHz FSB.. so it makes sense that nothing breaks between the two. 40 MHz FSB is for a DX2 80.. is that what you're going after?

For the record I also never found a VLB card that worked reliably above 33MHZ FSB... Not IO not VGA...

I am using a UMC U5S-40. The CL-GD5428 card I have in there works fine at 40MHz, so I am OK in terms of video cards..

appiah4 wrote on 2026-02-05, 06:31:

douglar wrote on 2026-02-04, 13:57:

I think you need to pay attention to the IDE controller on the card, not the floppy / multi-io controllers. […]
Show full quote

I think you need to pay attention to the IDE controller on the card, not the floppy / multi-io controllers.

I think Promise, CMD, W83759AF, SIS 601 and ADI2 based controllers generate their own strobe signals for the IDE cable, which gives them better reliability when talking to PATA devices as the VLB signal speed changes.

QDI, UMC and cards that use jumpers to set the IDE speed often generate their strobes for the IDE cable from the VLB signal, and this can make things more sensitive to any imperfections when the VLB speed increases.

If you are having trouble with a card that has speed jumpers, you can try setting a lower speed on the jumpers to see if that improves things.

Thank you, this is news to me. I have five VLB IO cards and they are all UMC, Goldstar or Winbond - various different ICs, but they all have speed setting jumpers and none of them seem to work reliably at 40MHz even at the slowest setting and extra wait states. I don't find it a huge problem in DOS, to be fair, to use an ISA IO card, but I guess it could have been an issue if I wanted to run Win32 on a 486.

I love my UMC U5S-40 setup, it is amazingly compatible for DOS and runs speed sensitive things like Ultima 7 and Theme Park super well. Not being able to fully upgrade it is making my inner OCD go crazy 🤣

What storage device are you using? Have you tried adding additional waits with the speed jumpers?

I have a VLB 486 DX4-120Mhz (40Mhz BUS) system that works fine with this Winbond IO card.

I used with the Motherboard and Orchid VGA showed on the second picture.

Admittedly I haven't tested extensively, I booted using an IDE to SD adapter into DOS and ran a few quick tests, but I bought these 3 parts together, they were all part of the same system, and supposedly ran together for a few decades.

douglar wrote on 2026-02-05, 14:53:

appiah4 wrote on 2026-02-05, 06:31:

douglar wrote on 2026-02-04, 13:57:

I think you need to pay attention to the IDE controller on the card, not the floppy / multi-io controllers. […]
Show full quote

I think you need to pay attention to the IDE controller on the card, not the floppy / multi-io controllers.

I think Promise, CMD, W83759AF, SIS 601 and ADI2 based controllers generate their own strobe signals for the IDE cable, which gives them better reliability when talking to PATA devices as the VLB signal speed changes.

QDI, UMC and cards that use jumpers to set the IDE speed often generate their strobes for the IDE cable from the VLB signal, and this can make things more sensitive to any imperfections when the VLB speed increases.

If you are having trouble with a card that has speed jumpers, you can try setting a lower speed on the jumpers to see if that improves things.

Thank you, this is news to me. I have five VLB IO cards and they are all UMC, Goldstar or Winbond - various different ICs, but they all have speed setting jumpers and none of them seem to work reliably at 40MHz even at the slowest setting and extra wait states. I don't find it a huge problem in DOS, to be fair, to use an ISA IO card, but I guess it could have been an issue if I wanted to run Win32 on a 486.

I love my UMC U5S-40 setup, it is amazingly compatible for DOS and runs speed sensitive things like Ultima 7 and Theme Park super well. Not being able to fully upgrade it is making my inner OCD go crazy 🤣

What storage device are you using? Have you tried adding additional waits with the speed jumpers?

It's a CF-IDE adapter, and I am considering trying an actual Hard Disk to see if that may help..

appiah4 wrote on 2026-02-05, 19:14:

It's a CF-IDE adapter, and I am considering trying an actual Hard Disk to see if that may help..

What CF are you using?
Did you try increasing the IDE active and recovery times using jumpers?
You could also try adding a VLB wait state using the 33/50 speed jumper.

douglar wrote on 2026-02-05, 20:22:

What CF are you using? Did you try increasing the IDE active and recovery times using jumpers? You could also try adding a VLB […]
Show full quote

appiah4 wrote on 2026-02-05, 19:14:

It's a CF-IDE adapter, and I am considering trying an actual Hard Disk to see if that may help..

What CF are you using?
Did you try increasing the IDE active and recovery times using jumpers?
You could also try adding a VLB wait state using the 33/50 speed jumper.

It's a 2GB Transcend, I don't remember the exact model.

I have already set the motherboard to >33MHz and enabled the 1WS jumper, to no avail.

I will try a real physical hard drive now, maybe the CF card or the IDE adapter may be too finnicky at higher FSBs..