The Monochrome Display Adapter (MDA, also MDA card, Monochrome Display and Printer Adapter, MDPA) is

IBM International Business Machines Corporation (using the trademark IBM), nicknamed Big Blue, is an American Multinational corporation, multinational technology company headquartered in Armonk, New York, and present in over 175 countries. It is ...

's standard video display card and

computer display standard Computer display standards are a combination of aspect ratio, display size, display resolution, color depth, and refresh rate. They are associated with specific expansion cards, video connectors, and monitors. History Various computer dis ...

for the

IBM PC The IBM Personal Computer (model 5150, commonly known as the IBM PC) is the first microcomputer released in the List of IBM Personal Computer models, IBM PC model line and the basis for the IBM PC compatible ''de facto'' standard. Released on ...

introduced in 1981. The MDA does not have any pixel-addressable graphics modes, only a single

monochrome A monochrome or monochromatic image, object or palette is composed of one color (or values of one color). Images using only shades of grey are called grayscale (typically digital) or black-and-white (typically analog). In physics, mon ...

text mode Text mode is a computer display mode in which content is internally represented on a computer screen in terms of characters rather than individual pixels. Typically, the screen consists of a uniform rectangular grid of ''character cells'', ea ...

which can display 80 columns by 25 lines of high-resolution text characters or symbols useful for drawing forms.

Hardware design

The original IBM MDA was an 8-bit ISA card with a Motorola 6845 display controller, 4 KB of

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, a DE-9 output port intended for use with an IBM monochrome monitor. A

parallel port In computing, a parallel port is a type of interface found on early computers ( personal and otherwise) for connecting peripherals. The name refers to the way the data is sent; parallel ports send multiple bits of data at once (paralle ...

for attachment of a printer is also included, avoiding the need to purchase a separate card.

Capabilities

The MDA was based on the IBM System/23 Datamaster's display system, and was intended to support business and

word processing A word processor (WP) is a device or computer program that provides for input, editing, formatting, and output of text, often with some additional features. Word processor (electronic device), Early word processors were stand-alone devices dedicate ...

use with its sharp, high-resolution characters. Each character is rendered in a box of 9 × 14

pixel In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a Raster graphics, raster image, or the smallest addressable element in a dot matrix display device. In most digital display devices, p ...

s, of which 7 × 11 depicts the character itself and the other pixels provide space between character columns and lines. Some characters, such as the lowercase "m", are rendered eight pixels across. The theoretical total screen

display resolution The display resolution or display modes of a digital television, computer monitor, or other display device is the number of distinct pixels in each dimension that can be displayed. It can be an ambiguous term especially as the displayed resoluti ...

of the MDA is 720 × 350 pixels, if the dimensions of all character cells are added up, but the MDA cannot address individual pixels to take full advantage of this resolution. Each character cell can be set to one of 256 bitmap characters stored in

ROM Rom, or ROM may refer to: Biomechanics and medicine * Risk of mortality, a medical classification to estimate the likelihood of death for a patient * Rupture of membranes, a term used during pregnancy to describe a rupture of the amniotic sac * ...

on the card, and this character set cannot be altered from the built-in hardware code page 437. The only way to simulate "graphics" is through

ASCII art ASCII art is a graphic design technique that uses computers for presentation and consists of pictures pieced together from the 95 printable (from a total of 128) character (computing), characters defined by the ASCII Standard from 1963 and ASCI ...

, obtaining a low resolution 80 × 25 "pixels" screen, based on character positions.

Code page 437 Code page 437 ( CCSID 437) is the character set of the original IBM PC (personal computer). It is also known as CP437, OEM-US, OEM 437, PC-8, or MS-DOS Latin US. The set includes all printable ASCII characters as well as some accented letters (di ...

has 256 characters (0-255), including the standard 95 printable

ASCII ASCII ( ), an acronym for American Standard Code for Information Interchange, is a character encoding standard for representing a particular set of 95 (English language focused) printable character, printable and 33 control character, control c ...

characters from (32-126), and the 33 ASCII control codes (0-31 and 127) are replaced with printable graphic symbols. It also includes another 128 characters (128-255) like the aforementioned characters for drawing forms. Some of these shapes appear in Unicode as

box-drawing characters Box-drawing characters, also known as line-drawing characters, are a form of semigraphics widely used in text user interfaces to draw various geometric frames and boxes. These characters are characterized by being designed to be connected horiz ...

. There are several attribute values - bit flags that can be set on each character on the screen. These are ''invisible, underline, normal, bright (bold), reverse video,'' and ''blinking''. Reverse video swaps the foreground and background colors, while blinking causes text to flash periodically. Some of these attributes can be combined, so that e.g. bright, underlined text can be rendered. Early versions of the MDA board have hardware capable of outputting red, green and blue TTL signals on the normally unconnected DE-9 video connector pins, theoretically allowing an 8-color display with a suitable monitor. The registers also allow the monochrome mode to be set on and off. No (widely) published software exists to actually control the feature. It is also possible to combine the values of output pins 7 (''Video)'' and 6 (''Intensity),'' to generate four brightness levels. ''Video'' corresponds to 2/3

luminance Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls wit ...

and ''Intensity'' to 1/3 luminance), but the actual display of these levels is monitor-dependent:

Use

The MDA was released alongside the IBM

Color Graphics Adapter The Color Graphics Adapter (CGA), originally also called the ''Color/Graphics Adapter'' or ''IBM Color/Graphics Monitor Adapter'', introduced in 1981, was IBM's first color graphics card for the IBM PC and established a De facto standard, de fac ...

, and can be installed alongside the CGA in the same computer. A command included with PC DOS permits switching the primary display between the CGA and MDA cards. Some software like

Lotus 1-2-3 Lotus 1-2-3 is a discontinued spreadsheet program from Lotus Software (later part of IBM). It was the first killer application of the IBM PC, was hugely popular in the 1980s, and significantly contributed to the success of IBM PC-compatibles ...

supports using both cards at the same time. Because of the lack of pixel-addressable graphics, MDA owners were unable to play PC games released with graphics support. However, textmode games were released for the PC (including text adventures) and at least one game, IBM's ''One Hundred And One Monochrome Mazes'', requires MDA. Box-drawing characters made the production of rudimentary graphics practical for early PC game titles, including

BBS door In a bulletin board system (BBS), a door is an interface between the BBS software and an external application. The term is also used to refer to the external application, a computer program that runs outside of the main bulletin board program. Som ...

games or titles such as '' Castle Adventure''. Another use for the MDA was as a secondary display for

debugging In engineering, debugging is the process of finding the Root cause analysis, root cause, workarounds, and possible fixes for bug (engineering), bugs. For software, debugging tactics can involve interactive debugging, control flow analysis, Logf ...

. Applications like

SoftICE SoftICE is a kernel mode debugger for DOS and Windows up to Windows XP. It is designed to run underneath Windows, so that the operating system is unaware of its presence. Unlike an application debugger, SoftICE is capable of suspending all oper ...

and the Windows debugger permitted the simultaneous use of an MDA and another graphics card, with the MDA displaying a debugger interface while the other card was showing the primary display.

Disadvantage

A typical 8-bit monochrome card could turn the 16-bit 8 MHz ISA bus into an 8-bit 4 MHz PC bus, which resulted in having the bus bandwidth cut by up to 75%. If the monochrome card was added to the PC as a second card besides a normal

VGA Video Graphics Array (VGA) is a video display controller and accompanying de facto graphics standard, first introduced with the IBM PS/2 line of computers in 1987, which became ubiquitous in the IBM PC compatible industry within three years. T ...

card for debugging purposes, this resulted in slow VGA performance. Microsoft recommended in its ''Writing HOT Games for Microsoft Windows'' (1994) to remove the monochrome card in such a setup for maximum speed of the VGA card.

Reception

The author of an internal IBM publication stated in October 1981 that he had planned to purchase the CGA adapter but changed his mind after seeing its poor display quality. Describing MDA as beautiful, he observed that "you stare at text a whole lot more than you stare at color graphics". MDA was more popular than CGA for business applications. The higher resolution of MDA's text and inclusion of a printer port made it more appealing for the business applications that were the focus of the original PC. However, dissatisfaction with its limitations quickly led to third parties releasing competing hardware. A well known example was the

Hercules Graphics Card The Hercules Graphics Card (HGC) is a computer graphics controller formerly made by Hercules Computer Technology, Inc. that combines IBM's text-only MDA display standard with a bitmapped graphics mode, also offering a parallel printer port. ...

. Introduced in 1982, it offered both an MDA-compatible high resolution text mode and a monochrome graphics mode. The founder of Hercules Computer Technology, Van Suwannukul, created the Hercules Graphics Card so that he could work on his

doctoral thesis A thesis (: theses), or dissertation (abbreviated diss.), is a document submitted in support of candidature for an academic degree or professional qualification presenting the author's research and findings.International Standard ISO 7144: D ...

on an

using the

Thai alphabet The Thai script (, , ) is the abugida used to write Thai, Southern Thai and many other languages spoken in Thailand. The Thai script itself (as used to write Thai) has 44 consonant symbols (, ), 16 vowel symbols (, ) that combine into at leas ...

, which was impossible at the low resolution of CGA or the fixed character set of MDA. It could address individual pixels, and displayed a black and white picture of 720 × 348 pixels. This resolution was superior to the CGA card, yet offered pixel-addressable graphics, so despite lacking color capability, the Hercules adapter's offer of high resolution bitmap graphics combined with MDA-grade text quality made it a popular choice, which was even shipped with many clones.

Specifications

MDA cards used a DE-9 output port intended for a digital TTL monitor, like the IBM monochrome monitor. The signal had the following specifications: * Type: Digital, TTL * Resolution: 720 × 350 * Horizontal frequency: 18.432 kHz * Vertical frequency: 50 Hz * Colors: Monochrome, with 2 to 4 intensity levels (depending on monitor)

Clone boards

Other boards offer MDA compatibility, although with differences on how attributes are displayed or the font used. *3270 PC *Amstrad PPC / PC20 *

Control Systems A control system manages, commands, directs, or regulates the behavior of other devices or systems using control loops. It can range from a single home heating controller using a thermostat controlling a domestic boiler to large industrial co ...

Artist 1 * Tamarack Microelectronics TD3088A3

References

{{IBM personal computers Monochrome Display Adapter

Monochrome Display Adapter The Monochrome Display Adapter (MDA, also MDA card, Monochrome Display and Printer Adapter, MDPA) is IBM's standard video display card and computer display standard for the IBM PC introduced in 1981. The MDA does not have any pixel-addressable ...

Computer display standards Graphics cards Computer-related introductions in 1981