[accrual]

Yes, the earliest mainboards I know of with on-board I/O including ATA is around Socket 5, the first mainstream Pentium boards. Some slightly older Socket 4 boards (circa 1994) have on-board I/O, but they weren't as common.

My 486 and earlier systems have all I/O provided by ISA cards, other than the 5-pin DIN keyboard port which was standard since the original PC.

[roryirvine]

I remember my dad's Dell 486P/33 from 1991 had integrated IDE, but that was a fairly high-end machine at the time (the forerunner of their "Precision" workstation range).

Details here: https://theretroweb.com/motherboards/s/dell-system-486p

But, yes, most bog standard machines would've had a separate "SuperIO" card containing serial, parallel, and IDE interfaces until the mid 90s.

[accrual]

Wow! Very impressive board, I had no idea. It's kinda cool how we can directly see some of the chips that would be on the SuperIO card but directly on the mainboard. Thanks for sharing.

[hakfoo]

White box systems didn't really acquire onboard I/O til the late 486/early 586 era, but it was pretty common on name-brand systems to integrate IDE/floppy/serial/parallel and usually video.