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You must mean EGA when you write VGA? VGA is based on EGA and VGA was not originally even a card like EGA was, but integrated on motherboard. EGA was a card and after VGA was introduced, it was only later available on a card.Justme– Justme2024-02-07 12:13:37 +00:00Commented Feb 7, 2024 at 12:13
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I suspected something like this, but have you got any materials showing that multi-adapter systems were an explicitly supported setup?user3840170– user38401702024-02-07 12:17:29 +00:00Commented Feb 7, 2024 at 12:17
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@user3840170 Supported setup by whom, and what kind of material? It was pretty common. IBM PC 5150 allowed you to have both CGA and MDA in the system. And people developing e.g. games used VGA for actual display and MDA or Hercules as the monochrome adapter for debugging.Justme– Justme2024-02-07 12:23:56 +00:00Commented Feb 7, 2024 at 12:23
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1@user3840170 it is mentioned in the original technical reference, see my answer.Stephen Kitt– Stephen Kitt2024-02-07 12:31:36 +00:00Commented Feb 7, 2024 at 12:31
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1@user3840170 Look at the DIP configuration instructions for the IBM EGA card: It explains how to set the switches if a second card is present or not. Furthermore, the assignment of different memory and I/O ranges is a strong indication that hardware support for a dual video-card setup was already considered before the PC hit the market. Note that neither card satisfies all requirements at that time: The MDA card couldn't display any kind of graphics beyond ASCII/CP437 art, and the CGA card couldn't display text at decent quality (because of TV compatibility).Michael Karcher– Michael Karcher2024-02-08 07:00:43 +00:00Commented Feb 8, 2024 at 7:00
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