INT 10H

INT 10h, INT 10H or INT 16 is shorthand for BIOS interrupt call 10hex, the 17th interrupt vector in an x86-based computer system. The BIOS typically sets up a real mode interrupt handler at this vector that provides video services. Such services include setting the video mode, character and string output, and graphics primitives (reading and writing pixels in graphics mode).

To use this call, load AH with the number of the desired subfunction, load other required parameters in other registers, and make the call. INT 10h is fairly slow, so many programs bypass this BIOS routine and access the display hardware directly. Setting the video mode, which is done infrequently, can be accomplished by using the BIOS, while drawing graphics on the screen in a game needs to be done quickly, so direct access to video RAM is more appropriate than making a BIOS call for every pixel.

Furthermore, on a modern x86 system, BIOS calls can only be performed in Real mode, or Virtual 8086 mode. v8086 is not an option in Long mode. This means that a modern operating system, which operates in Protected mode (32 bit), or Long mode (64 bit), would need to switch into real mode and back to call the BIOS - a hugely expensive operation. Although most modern systems typically use device drivers that directly set the video mode, it is not feasible for hobbyist systems to have a device driver for every video card - a problem that also plagues older, unsupported systems such as Windows 98. Such systems instead can drop into Real mode to switch the video mode, then draw to the framebuffer directly.

List of supported functions

The list is incomplete; use Ralf Brown's list for comprehensive information. Please only add IBM/PC or other common standard functions. 00h through 0fh are CGA.

Function Function code Parameters Return
Set video mode AH=00h AL = video mode AL = video mode flag / CRT controller mode byte
Set text-mode cursor shape AH=01h CH = Scan Row Start, CL = Scan Row End

Normally a character cell has 8 scan lines, 0-7. So, CX=0607h is a normal underline cursor, CX=0007h is a full-block cursor. If bit 5 of CH is set, that often means "Hide cursor". So CX=2607h is an invisible cursor.

Some video cards have 16 scan lines, 00h-0Fh.

Some video cards don't use bit 5 of CH. With these, make Start>End (e.g. CX=0706h)
Set cursor position AH=02h BH = Page Number, DH = Row, DL = Column
Get cursor position and shape AH=03h BH = Page Number AX = 0, CH = Start scan line, CL = End scan line, DH = Row, DL = Column
Read light pen position (Does not work on VGA systems) AH=04h AH = Status (0=not triggered, 1=triggered), BX = Pixel X, CH = Pixel Y, CX = Pixel line number for modes 0Fh-10h, DH = Character Y, DL = Character X
Select active display page AH=05h AL = Page Number
Scroll up window AH=06h AL = lines to scroll (0 = clear, CH, CL, DH, DL are used),

BH = Background Color and Foreground color. BH = 43h, means that background color is red and foreground color is cyan. Refer the BIOS color attributes

CH = Upper row number, CL = Left column number, DH = Lower row number, DL = Right column number
Scroll down window AH=07h like above
Read character and attribute at cursor position AH=08h BH = Page Number AH = Color, AL = Character
Write character and attribute at cursor position AH=09h AL = Character, BH = Page Number, BL = Color, CX = Number of times to print character
Write character only at cursor position AH=0Ah AL = Character, BH = Page Number, CX = Number of times to print character
Set background/border color AH=0Bh, BH = 00h BL = Background/Border color (border only in text modes)
Set palette AH=0Bh, BH = 01h BL = Palette ID (was only valid in CGA, but newer cards support it in many or all graphics modes)
Write graphics pixel AH=0Ch AL = Color, BH = Page Number, CX = x, DX = y
Read graphics pixel AH=0Dh BH = Page Number, CX = x, DX = y AL = Color
Teletype output AH=0Eh AL = Character, BH = Page Number, BL = Color (only in graphic mode)
Get current video mode AH=0Fh AL = Video Mode, AH = number of character columns, BH = active page
Change text mode character set[1] AH=11h BH = Number of bytes per character, CX = Number of characters to change, DX = Starting character to change, ES:BP = Offset of character data
Write string (EGA+, meaning PC AT minimum) AH=13h AL = Write mode, BH = Page Number, BL = Color, CX = Number of characters in string, DH = Row, DL = Column, ES:BP = Offset of string
set VESA-Compliant video modes, beginning at 640 by 480 and reaching 1280 by 1024 with 256 colors AX=4f02h BX = video mode, if Sign bit (bit 15) set, video memory will not be refreshed
Other VESA VBE commands AX=4F00h to 4F15h See spec See spec
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See also

References
  1. "A Font changing routine". Forever Young Software. Retrieved March 8, 2020.
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