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MDA - the first video adapter for IBM PC computers

It was introduced by IBM in 1981 as a standard video adapter, as well as a standard for monitors connected to it. MDA did not support working in graphical mode. The only acceptable video mode was monochrome text mode (Video mode 7), in which a matrix of characters of 80 columns and 25 rows was displayed on the screen.

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Video modes with so many characters per line and lines on the screen have caught on; The result of this is, for example, that the Linux kernel sources are formatted so that each line contains no more than 80 characters, making them easy to view in text mode. To depict the character, a 9x14 pixel matrix was used, of which the visible part of the character was composed as 7x11, and the remaining pixels were used to form the empty space between the rows and columns. The standard MDA video adapter was based on the Motorola 6845 chip and equipped with 4 KB of video memory. The scanning frequency was 50 Hz, and a display with a long-lasting phosphor was recommended for operation.

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Each character could have the following attributes: invisible, underlined, normal, bright (bold), inverted, and blinking. Some of these attributes could be combined, and, for example, you could get text consisting of bright (bold) and underlined characters. Theoretically, the MDA screen resolution was 720×350 pixels. This figure can be obtained by multiplying the width of one character (9 pixels) by the number of columns (80) and the height of the character (14 pixels) by the number of rows (25).
However, the MDA video adapter was not capable of addressing individual pixels; it operated in text mode, in which one of 256 characters could be placed in each character space. MDA used the code page CP437. The character images were stored in the ROM of the video adapter, and there was no possibility of changing them programmatically. The only way to draw a “graphic picture” on the screen is to use ASCII or ANSI graphics. The original expansion card released by IBM contained, in addition to the MDA video adapter, a parallel port controller, and the full name of such a card was: “Monochrome Display and Printer Adapter” (MDPA) - a monochrome display and printer adapter. Using such a card saved the computer owner from having to buy a separate expansion card to connect the printer.

D-sub 9-pin (DE-9) connector on the video card. View of the contacts from the side of the plug-in mating connector. The first pin is at the top right, the ninth at the bottom left.

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