And actually, INT 13h is the BIOS interrupt to access block-based disk I/O functions (like sector read, track format, etc.). The INT used for mode-setting is 10h (with AH=00h and AL=13h as mode for 320x200 at 256 colors).

Thank you both for the corrections, I was a teen in the 90s so I could have had it wrong or misremembered.

I just looked up the 13h interrupt and you are absolutely right!