You don't mention, is this an integrated controller or add-in card (either ISA or VLB).

My 486 VLB system has no integrated IDE. I use an ISA card with one channel, and I slave my CD-ROM drive to my hdd. It works for me. But if I wanted 2 channels, I'd have to upgrade the controller card.

No, it's not integrated. I have actually never seen any VLB mobo with an integrated controller (maybe one PCI-VLB combo has it).

I have couple of external VLB controllers: one Promise, one UMC and some other one. One of them has two sets of HDD headers.

So you assume that it's only a matter of the controller if you can use one or two channels? I thought it's also related to motherboard and BIOS (My BIOS is from Apr 1994)

I have a DTC M/I/O card with two IDE channels. The BIOS will use the primary one, and the others need a driver to be used, but good luck finding one.

I have an ISA two channel IDE controller. None of my 486 VLB is capable of using the second IDE channel and the card is working perfectly, I tested it in a Pentium machine.

The ASUS VL/I-486SV2G/GX4 manual states the following about IDE controllers:

System BIOS support for Enhanced IDE including up to four IDE hard disks or other IDE devices and support for hard disks larger than 528MB and up to 8.4GB. When used with a separate IDE controller card that supports Enhanced IDE, support for four IDE devices in two channels, faster data transfer rates and direct support for IDE devices such as Tape Backup and CD-ROM drives.

So it seems that dual-IDE feature must be supported by the BIOS in order to use the second channel in the controller card. Maybe the BIOS of your 486SVGO has no support for this. From the previous posts, it seems not many VLB motherboards can use the second channel of the card.

tikoellner wrote:

No, it's not integrated. I have actually never seen any VLB mobo with an integrated controller (maybe one PCI-VLB combo has it).

I have couple of external VLB controllers: one Promise, one UMC and some other one. One of them has two sets of HDD headers.

So you assume that it's only a matter of the controller if you can use one or two channels? I thought it's also related to motherboard and BIOS (My BIOS is from Apr 1994)

Quite lot LPX form factor 486 boards have VLB + onboard IDE like this one.

Thank you guys. It seems like my intuition was wrong.

And how about I get some IDE controller with internal BIOS supporting two channels? Will that "override" this limitation?

Not sure, from the bit of the manual you quoted above it sounds like it though.
Another option which was common back then is to use a soundcard with an IDE channel, It'll only support CD drives though, not HDD's

tikoellner wrote:

Thank you guys. It seems like my intuition was wrong.

And how about I get some IDE controller with internal BIOS supporting two channels? Will that "override" this limitation?

If you mean a IDE controller with its own BIOS chip, I think so, but you'll have to disable the motherboard IDE controller (if that is possible) for it to work.