VESA BIOS Extensions (VBE) is a VESA standard, currently at version 3, that defines the interface that can be used by software to access compliant video boards at high resolutions and bit depths. This is opposed to the "traditional" INT 10h BIOS calls, which are limited to resolutions of 640ÃÂ480 pixels with 16 colour (4-bit) depth or less. VBE is made available through the video card's BIOS, which installs some interrupt vectors that point to itself during boot up.
Most newer cards implement the more capable VBE 3.0 standard. Older versions of VBE provide only a real mode interface, which cannot be used without a significant performance penalty from within protected mode operating systems. Consequently, the VBE standard has almost never been used for writing a video card's drivers; each vendor has thus had to invent a proprietary protocol for communicating with its own video card. Despite this, it is common that a driver thunk out to the real mode interrupt in order to initialize screen modes and gain direct access to a card's linear frame buffer, because these tasks would otherwise require handling many hundreds of proprietary variations that exist from card to card.
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.
Initially, the need for standardization came from problems with accessing higher than standard VGA resolutions and color-depth modes on Super VGA graphic cards. Using those modes with cards produced by different manufacturers required drivers, which were available only for a few programs (mainly AutoCAD and Windows), while majority of the software was still made for DOS. The VBE allowed developers of DOS real-mode applications to use the new graphic modes in a common, standardized way.
VBE 1.0 (VS891001) was defined in 1989. VBE 1.1 (VS900602) was defined in 1990. VBE 1.2 (VS911022) was defined in 1991. These versions of VBE require real mode to work.
VBE defines several new functions called through INT 10H. The function numbering start with AX=4F00, or (AH=4F, AL=00), for Function 00h. 00h to 05h were defined in VBE 1.0, 06h and 07h in 1.1, and 08h in 1.2.
This standard provides the primary functionality of the VESA BIOS Extensions. It allows applications to determine the capabilities of the graphics card and provides the ability to set the display modes that are found. VBE 2.0 adds some new features above the prior VBE 1.2 standard including linear framebuffer access and protected mode banking. Some of the VBE Core 2.0 features include:
A superset of the VBE 2.0 standard. This standard adds refresh rate control, facilities for stereo glasses, improved multi-buffering and other functions to the VBE 2.0 standard.
A new "Protected Mode Entry Point" was added as an alternative to Function 0Ah. This gives access to all the VBE functions, thus allowing things like changing the graphics mode or setting the logical scan line length from protected mode, which were not possible with the old Function 0Ah.
VBE/AF provides a low-level, standard interface to common acceleration functions available on most hardware. Some of the functions defined in the standard are access to hardware cursors, Bit Block Transfers (Bit Blt), off screen sprites, hardware panning, drawing and other functions. It is defined to work under 32-bit protected mode. Despite the widespread adoption of VBE Core, very few devices support VBE/AF. The FreeBE/AF project implements free third-party VBE/AF drivers for certain graphics cards.
Supplemental specifications provides device independent interface between application software and Super VGA hardware. Function numbers are assigned by VESA Software Standards Committee (SSC).
DPMS is a hardware standard that allows graphics cards to communicate with DPMS-compliant monitors via a special signalling system that can be used with existing graphics controllers and monitor cables. This signalling system allows the graphics card to tell the monitor to go into a number of different power management or power saving states, which effectively allow the monitor to turn itself off when it is not in use.
Allows access to special features in flat panel controllers.
Provides standard to audio services.
Currently (version 1.00), the VBE/AI specification defines three device classes: WAVE, MIDI, and VOLUME. Device types not covered:
Provides standard entry to vendor-specific extensions.
The Display Data Channel or DDC is a digital connection between a computer display and a graphics adapter that allows the display to communicate its specifications to the adapter. The standard was created by VESA.
Provides hardware independent means for operating system and application to read and write data over IòC serial control interface.
Although mode number is a 16-bit value, the optional VBE mode numbers are 14 bits wide. Bit 15 is used by VGA BIOS as a flag to clear or preserve display memory. VBE defined mode numbers as follows:
Starting in VBE/Core 2.0, VESA no longer defines new VESA mode numbers and no longer requires a device to implement the old numbers. To properly detect information of a screen mode, use Function 01h - Return VBE Mode Information.
Mode 81FFh is a special video mode designed to preserve current memory contents and give access to the entire video memory.
Beginning with the VBE 2.0 standard, no new modes will be defined by VESA, and old modes are no longer mandatory. The use of defined modes should be considered deprecated: modern video cards may or may not use these mode numbers (even though most do for backward compatibility), and modern software should not use them. The correct way for software to discover available display modes is to obtain a list of modes (using "Function 00h - Return VBE Controller Information") and then to check each mode (using "Function 01h: Return VBE Mode Information") until it finds the mode/s it requires.
Modes 264âÂÂ268 are text modes. 264 (0108h) is 80 columns à60 rows (80ÃÂ60), 265 (0109h) is 132ÃÂ25, 266 (010Ah) is 132ÃÂ43, 267 (010Bh) is 132ÃÂ50 and 268 (010Ch) is 132ÃÂ60.
The table below combines the modes defined by VESA (the values denoted in black) along with modes commonly used, but which may not work on all graphics cards as they are not defined by any standard ().
A few tools have been written to detect VBE modes available on a system. They generally work by invoking Function 01h, which is more reliable than assuming a table of extended modes as it's part of the device's self-documentation.
The Linux kernel allows the user to select the VESA mode at boot time by passing a code in memory to the kernel. The LILO boot loader passes this code based on a "vga" parameter in its configuration file. It takes the form 'vga=XXX', where XXX is the decimal value, or 'vga=0xHHH', where HHH is the hexadecimal value. However, the 'vga=' boot loader parameter does not directly accept VESA video mode numbers; rather, the Linux video mode number is the VESA number plus 512 (in the case of the decimal representation) or plus 0x200 (in the case of the hexadecimal representation). For example, the defined VESA value of 257 (0x101), representing 640x480 and 256 colours, has an equivalent Linux video mode value of 769 (0x301).
As indicated earlier, the VESA standard defines a limited set of modes; in particular, none above ÃÂ are covered and, instead, their implementation is completely optional for graphics adapter manufacturers. As vendors are free to utilize whatever additional values they please, this means that, in the table below, the modes (and expressed in decimal form) may not apply to every graphics adapter!
<small>1: 32-bit is really (8:8:8:8), but the final 8-bit number is an "empty" alpha channel. It is otherwise equal to 24-bit colour. Many GPUs use 32-bit colour mode instead of 24-bit mode merely for faster video memory access through 32-bit memory alignment.</small>
VGA= also appears to select ÃÂ800 (8-bit) for various laptops' displays. <br> VGA= is ÃÂ
The VESA BIOS emulation in the Parallels virtual machine has a different set of non-standard VESA modes. As of build 3214, LRMI vbetest reveals these modes:
The VESA BIOS emulation in the VirtualBox virtual machine has a different set of non-standard VESA modes. As of 6.1.38_Ubuntu build r153438, the VESA BIOS function AX=0x4F01 reveals these modes (See also VBETables-gen.c):