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Encyclopedia > Monochrome Display Adapter
Green screen driven by a Monochrome Display Adapter
Green screen driven by a Monochrome Display Adapter

The Monochrome Display Adapter (MDA, also MDA card, Monochrome Display and Printer Adapter, MDPA) introduced in 1981 was IBM's standard video display card and computer display standard for the PC. The MDA did not have any graphics mode of any kind; it only featured a single monochrome text mode (PC video mode 7), which could display 80 columns by 25 lines of high resolution text characters. Download high resolution version (1024x740, 91 KB) IBM PC 5150 with keyboard and green monochrome monitor (5151), running MS-DOS 5. ... Download high resolution version (1024x740, 91 KB) IBM PC 5150 with keyboard and green monochrome monitor (5151), running MS-DOS 5. ... The IBM PC with green screen Green screen was the common name for a monochrome CRT computer display using a green P1 phosphor screen. ... 1981 (MCMLXXXI) was a common year starting on Thursday of the Gregorian calendar. ... International Business Machines Corporation (IBM, or colloquially, Big Blue) (NYSE: IBM) (incorporated June 15, 1911, in operation since 1888) is headquartered in Armonk, New York, USA. The company manufactures and sells computer hardware, software, and services. ... It has been suggested that Display standard be merged into this article or section. ... IBM PC (IBM 5150) with keyboard and green screen monochrome monitor (IBM 5151), running MS-DOS 5. ... Something which is monochromatic has a single color. ... A text mode program communicates with the user by only displaying text and possibly a limited set of predefined semi-graphical characters, which allow the drawing of rudimentary boxes around portions of text, either to highlight the content or to simulate widget or control interface objects found in GUI programs. ...


The standard IBM MDA card was equipped with 4 kilobytes of video memory. The MDA's high character resolution (sharpness) was a feature meant to facilitate business and wordprocessing use: Each character was rendered in a box of 9×14 pixels, of which 7×11 made out the character itself (the other pixels being used for space between character columns and lines). Bold textItalic text [edit] Headline text A kilobyte (derived from the SI prefix kilo-, meaning 1000) is a unit of information or computer storage equal to either 1024 or 1000 bytes. ... VRAM an acronym for Video RAM. Generally a term used in computers to describe RAM dedicated to the purpose of displaying bitmap graphics in raster graphics hardware. ... This example shows an image with a portion greatly enlarged, in which the individual pixels are rendered as little squares and can easily be seen. ...


The MDA featured the following character display attributes: invisible, underline, normal, bright (bold), reverse video, and blinking; some of these attributes could be combined, so that e.g., bright, underlined text could be produced.


The theoretical total screen resolution of the MDA was 720×350 pixels. This number is arrived at through calculating character width (9 pixels) by columns of text (80) and character height (14 pixels) by rows of text (25). However, the MDA again could not address individual pixels; it could only work in text mode, limiting its choice of display patterns to 256 characters. Its character set is known as code page 437. The character patterns were stored in ROM on the card, and so could not be changed by software. The only way to produce "graphical" screen content would have been through ANSI art. IBM PC or MS-DOS code page 437, often abbreviated CP437 and also known as DOS-US or OEM-US, is the original character set of the IBM PC, circa 1981. ... Read-only memory (ROM) is a class of storage media used in computers and other electronic devices. ... A screenshot of TheDraw editing an ANSI art picture of a shuttle; the purple text blinks ANSI art is a computer artform that was widely used at one time on BBSes. ...


IBM's original MDA included a parallel printer port (hence its original name of "Monochrome Display and Printer Adapter"), thus avoiding the need for a separate parallel interface on computers fitted with an MDA. In computing, a parallel port is a type of physical interface used in conjunction with a cable to connect separate peripherals in a computer system. ...

Contents

Specifications

Connector

Pin numbers (looking at socket):


Image File history File links DE9_Diagram. ...

Pin assignments[1]
Pin Function
1 Ground
2 Ground
3 Not Used
4 Not Used
5 Not Used
6 Intensity
7 Video
8 Horizontal Sync
9 Vertical Sync

Signal

Type Digital, TTL
Resolution 640h × 350v
H-freq 18.432kHz
V-freq 50Hz
Colors 2-4[2]

Competing adapters

There were two commonly available competing display adapters:

  • For PC users requiring bitmapped graphics and/or color, IBM offered its Color Graphics Adapter (CGA, also CGA card), launched at the same time as their MDA. The CGA was originally more expensive and intended as a higher end solution, however the lower resolution of its text mode characters (as compared to MDA) made CGA cards less attractive for business use.
  • Introduced in 1982, the non-IBM Hercules Graphics Card (also HGC) offered both an MDA compatible high resolution text mode and a monochrome graphics mode. It could address individual pixels and display a black and white picture of 720×348 pixels. This resolution was better than even the highest monochrome resolution CGA cards could offer. Thus, even without a colour capability of any kind, the Hercules adapter's offer of monochrome graphics without sacrificing MDA-equivalent text quality made it a more desirable choice for many.

For the use of the term raster in radio regulation, see frequency raster. ... The Color Graphics Adapter (CGA), introduced in 1981, was IBMs first color graphics card, and the first color computer display standard for the IBM PC. The standard IBM CGA graphics card was equipped with 16 kilobytes of video memory. ... 1982 (MCMLXXXII) was a common year starting on Friday of the Gregorian calendar. ... The Hercules Graphics Card (HGC) was a mid-1980s computer graphics controller which through its popularity became a de-facto display standard. ...

See also

The IBM PC with green screen Green screen was the common name for a monochrome CRT computer display using a green P1 phosphor screen. ... This page meets Wikipedias criteria for speedy deletion. ...

References

  1. ^ IBM Personal Computer Hardware Library: Technical Reference (Revised edition, 1983)
  2. ^ There are four possible combinations of values for the 'Intensity' and 'Video' pins, but not all monitors will display them as four distinct intensity levels.

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Monochrome Display Adapter Notes (2385 words)
The two big chips on an MDA are the 6845 (soldered on) and the character generator ROM (usually socketed).
For Hercules-compatible cards (which are a superset of MDA), bit 7 is a vertical sync signal (1 when the screen is being drawn, 0 in the vertical blanking interval) and bit 1 returns lightpen status.
The resolution is the same as a normal MDA (720x350) but the font used is based on the 3270 terminal rather than the original MDA.
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