Detect CGA, EGA, VGA or VESA BIOS in DOS.

detect.asm

format MZ
entry main:start
use16

segment main

start:
	; detect EGA BIOS
	mov ah, 0x12
	mov bl, 0x10
	int 0x10
	cmp bl, 0x10
	je .cga
	; detect VGA BIOS
	mov ax, 0x1a00
	int 0x10
	cmp al, 0x1a
	jne .ega
	; detect VESA BIOS
	mov ax, vesa_info_buffer
	mov es, ax
	xor di, di
	mov ax, 0x4f00
	int 0x10
	cmp ax, 0x004f
	jne .vga
	cmp word [es:di+0], 0x4556  ; 'VE'
	jne .vga
	cmp word [es:di+2], 0x4153  ; 'SA'
	jne .vga
	cmp word [es:di+4], 0x0102  ; version
	jb .vga
.vesa:
	mov dx, strings.vesa
	jmp .print
.vga:
	mov dx, strings.vga
	jmp .print
.ega:
	mov dx, strings.ega
	jmp .print
.cga:
	mov dx, strings.cga
.print:
	mov ax, strings
	mov ds, ax
	mov ah, 0x09
	int 0x21
	mov ax, 0x4c00
	int 0x21

segment strings
	.cga db "CGA$"
	.ega db "EGA$"
	.vga db "VGA$"
	.vesa db "VESA$"

segment vesa_info_buffer
	rb 256

Thanks, very useful. Your comment about VESA should make it clearer that you're trying to detect VESA SVGA and not VESA XGA. Only for the sake of completeness.