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The PS/2 chipset's limited abilities prevent EGA compatibility and high-resolution multi-color VGA display modes. The tenure of MCGA was brief; the PS/2 Model 25 and Model 30 were discontinued by 1992, and the only manufacturer to produce a clone of this display adapter was Epson , in the Equity Ie and PSE-30 , since the VGA standard introduced ...
Mode 13h is something of a curiosity, because the VGA is a planar device from a hardware perspective, and not suited to chunky graphics operation. The VGA has 256 KiB of video memory consisting of 4 banks of 64 KiB, known as planes (or 'maps' in IBM's documentation).
In the 10-color multicolor mode, a single pixel of every 4×8 block (a character cell) may have any of four colors: the background color, the auxiliary color (both shared for the entire screen and selectable among the entire palette), the same color as the overscan border (also a shared color) or a free foreground color, both selectable among ...
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.
Other common display modes also defined as VGA include 320×200 at 256 colours (8 bpp) (standard VGA resolution for DOS games that stems from halving the pixel rate of 640×400, but doubling color depth) and a text mode with 720×400 pixels; these modes run at 70 Hz and use non-square pixels, so 4:3 aspect correction is required for correct ...
Each screen character is represented by two bytes aligned as a 16-bit word accessible by the CPU in a single operation. The lower (or character) byte is the actual code point for the current character set, and the higher (or attribute) byte is a bit field used to select various video attributes such as color, blinking, character set, and so forth. [6]
One range of the palette was many brightnesses of one primary color (say green), and another range of the other two primaries mixed together at different amounts and brightnesses (red and blue). It effectively reduced the horizontal resolution by half, but allowed a 12-bit "true color" in DOS and other 8-bit VGA/SVGA modes.
Fonts are stored as bitmaps at a color depth of 1-bit, with a "1" representing the character and a "0" representing the background. These colors can be chosen independently, for each character on the screen, from the full 16-color CGA palette. The character set is defined by hardware code page 437.