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Great Hierophant
December 30th, 2008, 09:01 PM
I have IBM's EGA card and VGA card. They are rare and obviously extremely important for founding graphics standards. I am concerned today with their backwards compatibility with IBM's earlier CGA adapter (which I also have.)

In a previous post, I asked fellow members to comment on the compatibility of the Tandy 1000 video controllers (non-VGA) with IBM's CGA card, and here are the results:
http://www.vintage-computer.com/vcforum/showthread.php?t=12922

I decided to put my EGA and VGA cards inside my IBM PC 5150 and test them with several games that "tweak" the CGA in ways described in my previous post. However, instead of giving detailed results, I will say that these cards performed abysmally in games that utilize the CGA hardware registers directly. However, for laughs:

RGB Tests

1. Games that use tweaked text modes as graphics modes

Will not work correctly unless the game specifically supports using the EGA or VGA cards. Windmill Software's games, even those that do not use tweaked text modes, will not run properly on EGA and VGA cards. Ditto for other games (except Icon: Quest for the Ring and The Seven Spirits of RA, which support EGA.)

2. Changing Intensity in 4-color palette modes & Support for green/red/brown and cyan/magenta/white palette

The IBM VGA technical reference states that there are two palettes, 0 and 1. Palette 0 gives light cyan, light magenta and white (high intensity), palette 1 gives green, red and brown. This strongly implies that the intensity of the palettes cannot be changed. Intensity cannot be changed in the BIOS.

4. Changing border color in text modes.

Support should be present if the BIOS is used.

5. Changing foreground color in 640x200 mode

I didn't test this, but the IBM VGA Technical Reference states the foreground color will be white. However, the BIOS will allow an EGA or VGA card to change the foreground or background color, but does nothing with a CGA card.

6. Support for the red/cyan/white palette

None

7. Games that change the palette or background color in mid-frame

Will not work, even on a 4.77MHz machine

8. Blink attribute/16 background colors in text modes

Implemented differently on EGA/VGA, will not work the same way as on a CGA card.