I have been unsuccessful with SiS 486/497 and UMC 8881/8886 DMA on onboard IDE. There was one post which indicated success with DMA on ALI 1487, however I was unsuccessful on the same ALI chipset.

There are reports that the latest version of SiS 496 supports EDO and tested to work. I think it was on a Lucky Star LS486-something motherboard. That is the only board I've seen this revision of the SiS 496 chipset. I have not tested it personally. Another user showed that EDO worked well on ALI 1486, however it seemed to me as the BIOS was just doing a little trick with RAM wait states to appear as if EDO was faster. FPM on SIS 486 and UMC 8881 area bout the same speed as EDO on the ALI. In short, there is little (no?) benefit of EDO on a 486 and it only causes issues with stability and timings.

I do not know the make of your motherboard. But if it has an AWARD BIOS and a DIP-style keyboard controller chip, it can be moddified to use native PS/2 mice.

Too bad your board doesn't sport nine DIP-32 cache sockets, for double-banked 1024K cache. That seems to be a requirement these days to spark my interest in PCI 486 boards. However, there is a good chance you can modify those DIP-28 sockets to be DIP-32 and wire them up for 1024K.

Concerning HDD limit - Sometimes 2 GB, sometimes 8 GB. Try it out and see. I find using a PCI or ISA DMA card for IDE or SCSI beneficial when using 486 boards. The onboard PIO IDE taxes the CPU too much and I never use onboard IDE PIO controllers in any of my setups.

I have a 486F55, but it's in storage right now. I'll try to fetch it this weekend and see if I can answer your questions.

Thanks for answers.
I still have this board in storage. Restoring is my future project for next year.
I don't want "ultimate" 486 with 5x86/160 and 1MB cache. I will use original DX4/120 CPU amd maybe cache upgraded to 512kB. I don't know if DX4 can run at 4x33 instad of 3*40) and if 13MHz more frequency is benefit with slower FSB. And i can't remember if my AMD was standard or Enhanced version.
Looking for EDO support because 16MB and bigger SIMMs are much easy to find compared to FPM.

After some research i solved two questions:

1. FREETECH is right. They has support website and produced many motherboards with "F" name. Like 486Fxx, 586F1x, P5Fxx, P6Fxx ...
Website is archived at Archive.org:
https://web.archive.org/web/19981207030605/ht … reetech.com:80/
dead FTP link: ftp://ftp.freetech.com/bios/486/f55_pci/

3.
https://web.archive.org/web/19981207030605/ht … RT/Download.htm
486F55 -- 486 PCI SiS 496/497 Chipset
55XS-G.EXE -- AWARD BIOS 06/03/96 Ver. G
sis49x.exe-- SiS 496/497 chipset IDE drivers
F55 Manual-- Motherboard manual in PDF

Sadly links are dead

https://web.archive.org/web/19990221053447/ht … BB/Tsvst217.htm

468 F55 use Flash BIOS chip?

And live links for both "F" and "G" BIOS versions
http://www.elhvb.com/supportbios.info/Archive … 6F55/index.html
Please archive files at vogons driver library.

Now i haven't only "sis49x.exe" IDE driver.
But for what OS is it?