> Был биос да биос, простой как семейные трусы, никому не мешал,

С кучей вендоро-расширений:
http://www.ctyme.com/intr/int-10.htm

InstallCheck:
For Ahead adapters, the signature "AHEAD" at C000h:0025h.
For Paradise adapters, the signature "VGA=" at C000h:007Dh.
For Oak Tech OTI-037/057/067/077 chipsets, the signature "OAK VGA" at
C000h:0008h.
For ATI adapters, the signature "761295520" at C000h:0031h; the byte
at C000h:0043h indicates the chipset revision:
31h for 18800
32h for 18800-1
...

багов:
http://www.ctyme.com/intr/rb-0069.htm (переключалка видеорежима)

,,,
[2] for ATI EGA Wonder, mode 08h is only valid if SMS.COM is loaded resident.
SMS maps mode 08h to mode 27h if the byte at location 0040:0063 is 0B4h,
otherwise to mode 23h, thus selecting the appropriate (monochrome or
color) 132x25 character mode.
for ATI VGA Wonder, mode 08h is the same, and only valid if VCONFIG loaded
resident
[3] early XGA boards support 132-column text but do not have this BIOS mode
[4] DESQview intercepts calls to change into these two modes (21h is page 0,
22h is page 1) even if there is no Hercules graphics board installed
[5] ATI BIOS v4-1.00 has a text-scrolling bug in this mode
[6] for AT&T VDC overlay modes, BL contains the DEB mode, which may be 06h,
40h, or 44h
...
[17] For 43-line text on EGA or 43/50-line text on VGA, you must load an 8x8
font using AX=1102h after switching to mode 3; VGA may also require
using INT 10/AH=12h/BL=30h

и воркароундов на воркароунде даже для достаточно простых вещей:
Int 10/AH=01h - VIDEO - SET TEXT-MODE CURSOR SHAPE
http://www.ctyme.com/intr/rb-0086.htm
> Notes: Buggy on EGA systems--BIOS remaps cursor shape in 43 line modes, but returns unmapped cursor shape.
> UltraVision scales size to the current font height by assuming
> ...
> Applications which wish to change the cursor by programming the hardware directly on EGA or above should call INT 10/AX=1130h or read 0040h:0085h first to determine the current font height. On some adapters, setting the end line greater than the number of lines in the font will result in the cursor extending to the top of the next character cell on the right
>
> BUG: AMI 386 BIOS and AST Premier 386 BIOS will lock up the system if AL is not equal to the current video mode

Предназначение "ненужной" абстракции в виде ОС -- в том числе и держать все эти обходные костыли для отдельных железок у себя под капотом, избавляя любого разработчика чего-то сложнее калькулятора, от необходимости держать в голове и переизобретать обход всех подводные камней сотен и тясяч  железяк:
https://github.com/torvalds/linux/search?q=quirks