INT 10H

Short description: BIOS interrupt call

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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 a hobbyist operating system 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, and then draw to the framebuffer directly.

In EFI 1.x systems, the INT 10H and the VESA BIOS Extensions (VBE) are replaced by the EFI UGA protocol. In widely used UEFI 2.x systems, the INT 10H and the VBE are replaced by the UEFI GOP.[1][2]

## List of supported functions

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

Function  | Function code  | Parameters  | Return

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Set video mode  | AH=00h  | AL = video mode

AL = video mode (For Old IBM Only)

| 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[3] | 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

## See also

* BIOS interrupt call
* Mode 13h
* VESA BIOS Extensions
* Ralf Brown's Interrupt List

## References

1. ↑ "What is efifb? — The Linux Kernel documentation". https://www.kernel.org/doc/html/latest/fb/efifb.html.
2. ↑ "What is vesafb? — The Linux Kernel documentation". https://www.kernel.org/doc/html/latest/fb/vesafb.html.
3. ↑ "A Font changing routine". http://www.fysnet.net/font.htm.

* INT 10h from Ralf Brown's Interrupt List, online version
* INT 10h on www.ousob.com

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