And since I listed all the books I used routinely I didn't know that.

Parent,

> I should know the answer to this, but was using the BIOS the only way to interact with hardware like disks, mice, and keyboard?

First link from your URL

> READ CHARACTER FROM STANDARD INPUT, WITH ECHO

Also drivers loaded via config.sys would extend MS-DOS, and be exposed via additional interrupts, e.g 0x33h for mices.

Now is interrupt 0x33h populated by MS-DOS, after loading a mouse driver configured in config.sys, still MS-DOS API or not?