Video Modes

Main

the MS-DOS operating system spanned nearly 20 years. This was during a timer period when advancements were being made incredibly quickly. Computers went from low resolution monochrome text only games and applications to high resolution Super VGA graphics with millions of colors in just over 10 years.

Due to the speed at which new video modes were being developed, it was common for games to be released with support for multiple video modes. The eXoDOS project is currently working through the games in an attempt to provide video mode options at launch, in order to be able to experience the game in all possible modes.

Video Modes

• Monochrome
• Hercules
• CGA
• PCjr
• Tandy
• EGA
• VGA
• SVGA

Monochrome

The Monochrome Display Adapter (MDA) was the base video card in the first 1981 IBM PC. it had a single mode that displayed 80 columns by 25 lines. There are currently no games in eXoDOS specifically set to use the MDA, as later cards were capable of displaying 80x25 text as well.

Hercules

The Hercules Graphics Card (HGC) was a monochrome card aimed at high resolution text. It was not common for games, however some games did have specific HGC drivers.

Modes:

• 80×25 text mode with 9×14 pixel font (effective resolution of 720×348)
• 720×348 graphics mode

CGA

The Color Graphics Adapter (CGA) was released alongside the original IBM PC in 1981 as an add-on card. It had 16 colors to choose from, but could only load a palette of 4 colors at a time. This led to many early CGA games having specific color combinations with red, yellow, green, and black being very common.

Graphics modes:

• 160×100 in 16 colors, chosen from a 16-color palette, utilizing a specific configuration of the 80x25 text mode.
• 320×200 in 4 colors, chosen from 3 fixed palettes, with high- and low-intensity variants, with color 1 chosen from a 16-color palette.
• 640×200 in 2 colors, one black, one chosen from a 16-color palette.
• Some software achieved greater color depth by utilizing artifact color when connected to a composite monitor.

Text modes:

• 40×25 with 8×8 pixel font (effective resolution of 320×200)
• 80×25 with 8×8 pixel font (effective resolution of 640×200)

PCjr

The IBM PCjr offered multiple CGA-compatible and enhanced modes built onto the system board.
Modes:

• 160x200 at 16 colors
• 320x200 at 16 colors
• 640x200 at 4 colors
  

The primary improvement over CGA is the greater color depth. CGA could only display 4 colors in its medium-resolution mode, and 2 colors in high-resolution. The PCjr increases these to 16 and 4 colors.

Tandy

The Tandy 1000 line of computers had it's own video mode. It started as a clone of the #PCjr, however it was enhanced and capable of displaying up to 16 colors at 320x200. It was also backwards compatible with most CGA modes.
In general, Tandy graphics were better than competing IBM PC models when it was first released. However the introduction of #EGA cards evened the capabilities.

CGA compatible modes:

• 320×200 in 4 colors from a 16 color (RGBI) hardware palette. Pixel aspect ratio of 1:1.2.
• 640×200 in 2 colors from 16. Pixel aspect ratio of 1:2.4
• 40×25 with 8×8 pixel font text mode (effective resolution of 320×200)
• 80×25 with 8×8 pixel font text mode (effective resolution of 640×200)

In addition to the CGA modes, it offers:

• 160×200 with 16 colors
• 320×200 with 16 colors
• 640×200 with 4 colors (from 16)

EGA

The Enhanced Graphics Adapter (EGA) released in 1984 as a replacement for CGA. EGA was standardized, allowing third-party cards to be created.
The EGA card allowed 16 colors simultaneously from a palette of 64 potential colors.

Graphics modes:

• 640×350 w/16 colors (from a 6 bit palette of 64 colors), pixel aspect ratio of 1:1.37.
• 640×350 w/2 colors, pixel aspect ratio of 1:1.37.
• 640×200 w/16 colors, pixel aspect ratio of 1:2.4.
• 320×200 w/16 colors, pixel aspect ratio of 1:1.2.

Text modes:

• 40×25 with 8×8 pixel font (effective resolution of 320×200)
• 80×25 with 8×8 pixel font (effective resolution of 640×200)
• 80×25 with 8×14 pixel font (effective resolution of 640×350)
• 80×43 with 8×8 pixel font (effective resolution of 640×344)

VGA

The Video Graphics Array (VGA) card was introduced in 1987 and quickly became the primary mode for gaming. It was the last video mode to be standardized, which meant most games of the era had support for it.
VGA allowed the simultaneous display of 256 colors.

Modes:

• 640×480 in 16 colors or monochrome
• 640×350 or 640×200 in 16 colors or monochrome (EGA compatibility)
• 320×200 in 256 colors (Mode 13h)
• 320×200 in 4 or 16 colors (CGA compatibility)

As the VGA began to be cloned in great quantities by manufacturers who added ever-increasing capabilities, its 640×480, 16-color mode became the de facto lowest common denominator of graphics cards. By the mid 1990s, a 640×480×16 graphics mode using the VGA memory and register specifications was expected by operating systems such as Windows 95 and OS/2 Warp 3.0, which provided no support for lower resolutions or bit depths, or support for other memory or register layouts without additional drivers. Well into the 2000s, even after the VESA standard for graphics cards became commonplace, the "VGA" graphics mode remained a compatibility option for PC operating systems.

SVGA

Super VGA (SVGA) was a non-standardized term for graphics cards that extended the VGA standards. SVGA was most commonly used to achieve 256 colors at a 640x480 resolution or 16 colors at 800x600 resolution. Attempts to standardize SVGA through VESA modes were attempted, however not all games supported this.
DOSBox generally emulated SVGA via the S3 Trio which supports VESA VBE 2.0, which was the last VESA standard before VESA VBE 3.0 which focused on Windows acceleration. Other SVGA garphics cards such as the Tseng Labs ET3000 & ET4000 series and the Paradise PVGA1A are also options. A no-line frame buffer hack (nolfb) mode is provided to emulate the ability to disable line buffer capability of the UniVBE utility.

References

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