Do you have in bios set Boot to SCSI option

It does sound like a problem with dma accesses. It may be a compatibility issue with the mobo chipset and CMD648. Frequently on 486 boards the PCI has essentially non functional DMA busmaster transfer support. But I have had a Promise Ultra66 at least working on a SiS 496 board.

Also, as far as I know, no 486 onboard ATA controllers support DMA. This first arrived with the Intel PIIX southbridge. The MS 98 driver should be fine any IDE controller.

I actually think you should try Win95 instead. Much faster on a 486.

I'd get a SCSI controller board for a 486. SCSI drivers were much faster than any other drives available at the time of the 486. If you're going to be playing any games that access the hard drive from time to time, like when you finish a level of a game and are waiting for the next level to load, you'll notice a big reduction in wait times.

It won't be easy though to find a SCSI drive that's quieter then their IDE versions though, but of course this depends solely on what the TS's personal preference is.
If IDE (or a PCI IDE controller) won't work whatsoever, then SCSI seems to be the best way out,

Do you have in bios set Boot to SCSI option

No, but i can to use scsi controller PCI after disable IDE onboard controller to boot on SCSI.

I only want to use my IDE harddrive with DMA ...

I don't know that i can't to use DMA on a 486, now i use the onboard IDE with the standard IDE driver (of windows98se) because there isn't windows98se drivers for the onboard IDE PB4 Abit.

When i will have a fast SCSI drive i will use SCSI

Thanx 😀

Ps: The IDE drivers (find in google) allow only 32bit access for dos/windows 3.1/Nt3.5/Os2/sco/unix there isn't DMA support...

Maybe the problem is which I take it that is a Asus CMD648 IDE?, It a PCI 2.1 spec and it Asus is RAID Controller.
You want look for a old Promise Ultra 33 card
Have you try using 40wire IDE cables and 80wire both ways?.
Have you try install the Windows 98 on that Controller and that Drive don't for get add the dos drivers to boot setup disc and win9x drivers.

When i use the PCI CMD-648, i can to boot to dos, i can to use it.
On windows, windows don't wan't to launch completly, and stop with black screen.

It's parhaps because i don't use the good drivers, i find it on google. The install menu say me drivers for PCI-64, and i reboot, i run windows ok when i don't boot on the PCI CMD-648 (without harddrive) and i use the onboard IDE controller for the harddrive.

Windows detect the card as au PCI Raid Udma controller.

one pic:
here

The IDE connectors are blue not black or me, but there is the same pic on the chip, i don't know what is the manufacturer? to find the good driver. But now i'm gooing tu use SCSI, i don't have again a sca to 68 scsi to use my sca hardrive but i buy it yesterday...