Dual channel basically means it has two IDE 'channels', or ports.
Each IDE port/channel can handle two drivers, a master and a slave, using a single cable. So you can connect 4 drives to it in total.
Later ISA IO controllers were generally dual channel, and most, if not all VLB controllers will be dual channel. Yours apparently is, because it has 2 connectors.

I've also got a Winbond W83787F based vlb controller with 2 IDE channels.

Unfortunately, since I use XT-IDE on that computer, I am not able to use the winbond drivers to take advantage of the VLB bandwidth, as the winbond drivers replace the disk bios with one that isn't compatible with large hard drives.

the winbond chip seems to be a standard io controller without any special thing

that "dual channel" thing may be related to the posibility to use up to 4 ide devices (two per "channel)
most cheap io controllers have one connector for up to two devices, so that may be the answer

according to this page http://www.ryston.cz/petr/vlb/qd6580.html
it seems to be due to the dual ide header only, the specs are just normal, nothing fancy

I've heard that with VLB controllers it actually makes sense to have two HDD drives connected to primary and secondary channels. First drive is used for the OS, second is for the games. I've never bothered to check the performance difference myself, though.

Some VLB I/O controllers have one IDE port running off of VLB and one IDE port running off of ISA.

So performance can be quite different depending on which port you use.

ISA is 16bit.
VLB is 32bit.

Yes, It does provide for faster data transfer with an EIDE supported hard-drive.
I think you have to select 32bit in your windows 3x settings too.

If your motherboard has VLB and you have a VLB controller or Video card I would use it.

Thanks a lot for the info, people! 😀