Do not know. You will not get any VLB IDE card running 100% stable at 66Mhz even with wait states AFAIK. Know of no ISA or VLB "EIDE controller at 66MHz too", not one was "Ultra ATA 66" because that came out in 1999 way after VLB so that leaves only PCI. Oh and am fairly sure that PCI standard was 33Mhz not 66mhz on 486, first pci-66mhz spec release was 1995 but implimented until later so doubt you will find 66mhz PCI on any 486 board. Good luck !
oops bad gramar

As for graphics cards, I was able to get my ARK1000VL cards working at 66MHz with 1ws. At that speed you definitely don't want any other VLB devices anyway. Best run your disk controller on ISA/EISA/PCI.

In your post you don't mention Socket/CPU type. All So4/So5 UMC Pentium chipsets support 66MHz bus speeds.

Support won't do much - you'll have to test if it's really working.

The UM888x boards that I tested were "perfectly" stable at 50mhz(+fastest timings) but after that things started falling apart. Timings is the main issue - pumping at high frequencies but with delay counts only to end up marginally faster or even slower is a bit fruitless.

I know about chipset 430NX Codename Neptune
It has got full features what I need
512MB Ram, 66MHz Host bus.
Unfortunately it is Intel. Do You know something about this?
I mean UMC 430NX?
I have read about few chips nearby 430 like 82C4xx by UMC
Maybe we do not have full information about UMC products from far east?

I am confused by your question. Are you interested in Pentium or 486 chipsets? Given by the motherboards you listed, you might be interested in 486 (Socket 3) boards.

Intel 430NX is a Pentium chipset. As mentioned above all Pentium chipsets (incl. UMC 8891AF/BF) have 66 MHz support (ok, some very early S4 boards might only support 60 MHz chips).

I don't believe any 486 MB has official 66 MHz support. No matter if using UMC or another chipset brand. Some might be configured to run at 66 MHz by more or less undocumented settings but you are likely to be in the off-spec (overclocking) territory. I don't think there is a 486 chip that needs 66 MHz bus so this is only for extreme overclocking (if at all useful).

Beside the unofficial 66MHz support, there also has to 1/2 PCI divider by BIOS or jumper.

Thanks. But could you tell me how much RAM handling?
UMC8891AF/BF
It looks very good.
I want it for new MSX model. DreamComp😀
My unofficial codename for new machine at this moment is MSX XP /experience.

Tymo486DX2 wrote on 2020-08-19, 20:23:

Thanks. But could you tell me how much RAM handling? UMC8891AF/BF It looks very good. I want it for new MSX model. DreamComp😀 My […]
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Thanks. But could you tell me how much RAM handling?
UMC8891AF/BF
It looks very good.
I want it for new MSX model. DreamComp😀
My unofficial codename for new machine at this moment is MSX XP /experience.

- The 430NX has a 512MB RAM limit according to wikipedia https://en.wikipedia.org/wiki/List_of_Intel_c … entium_chipsets .
- The UMC8891AF does not exist according to Google (may just be very obscure and forgotten)
- The UMC8891BF was used in the Giga-Byte GA-586AM motherboard (according to https://dependency-injection.com/early-pentium-chipsets/ ) , which supports 128MB RAM according to https://th99.infania.net/m/E-H/33070.htm . Chipset itself may support more .

I have found that chipsets' list
http://www.idhw.com/textual/guide/inst_mobo_a … rd_chipset.html

And another one , unfortunately intel
https://en.m.wikipedia.org/wiki/List_of_Intel_chipsets

I am very sorry that it is not UMC doc.

darry wrote on 2020-08-19, 20:39:

- The UMC8891AF does not exist according to Google (may just be very obscure and forgotten)

UMC8891AF (a part of a three-chip combination consisting of UMC8891AF,UMC8892AF and UM8886AF) actually does exist. AF means the first revision and BF the second revision of the chipset.

It appeared on motherboards like Biostar 8500UUR, Chicony CH-890C or Shuttle HOT-539 and perhaps others.

mpe wrote on 2020-08-19, 21:11:

darry wrote on 2020-08-19, 20:39:

- The UMC8891AF does not exist according to Google (may just be very obscure and forgotten)

UMC8891AF (a part of a three-chip combination consisting of UMC8891AF,UMC8892AF and UM8886AF) actually does exist. AF means the first revision and BF the second revision of the chipset.

It appeared on motherboards like Biostar 8500UUR or Shuttle HOT-539 and perhaps others.

Thank you for that . I just realized that the reason my search came up blank is that the actual part numbers on the chips are UM8891AF , UM8891BF , etc . There is no "C" .

max ram support is irrelevant if the motherboard cannot cache it. For 512MB of ram you need a lot of L2 cache, more then a 486 motherboard can support. I think the most ram a 486 board can cache is 128MB with 1MB of L2 cache - I might be wrong, but if I am somebody here will correct me.

Bye