VBE Mode Numbers
Although mode number is a 16-bit value, the optional VBE mode numbers are 14 bits wide. Bit 7 is used by VGA BIOS as a flag to clear or preserve display memory. VBE defined mode numbers as follows:
| Bit | Meaning |
|---|---|
| 0–8 | Mode numbers. If bit 8 is 1, it is a VESA defined VBE mode. |
| 9-10 | Reserved for expansion. Must be set to 0. |
| 11 | Refresh rate control Select. If set to 1, use user specified CRTC values for refresh rate, otherwise use BIOS default refresh rate. |
| 12–13 | Reserved for VBE/AF. Must be set to 0. |
| 14 | Linear/Flat Frame Buffer Select. If set to 1, use linear frame buffer, otherwise use banked frame buffer. |
| 15 | Preserve Display Memory Select. If set to 1, preserve display memory, otherwise clear display memory. |
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.
Read more about this topic: VESA BIOS Extensions
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