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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, each of which contains one of the characters of a character set; at the same time, contrasted to all points addressable (APA) mode or other kinds of computer graphics modes.

Text mode applications communicate with the user by using command-line interfaces and text user interfaces. Many character sets used in text mode applications also contain a limited set of predefined semi-graphical characters usable for drawing boxes and other rudimentary graphics, which can be used to highlight the content or to simulate widget or control interface objects found in GUI programs. A typical example is the IBM code page 437 character set.

An important characteristic of text mode programs is that they assume monospace fonts, where every character has the same width on screen, which allows them to easily maintain the vertical alignment when displaying semi-graphical characters. This was an analogy of early mechanical printers which had fixed pitch. This way, the output seen on the screen could be sent directly to the printer maintaining the same format.

Depending on the environment, the screen buffer can be directly addressable. Programs that display output on remote video terminals must issue special control sequences to manipulate the screen buffer. The most popular standards for such control sequences are ANSI and VT100.

Programs accessing the screen buffer through control sequences may lose synchronization with the actual display so that many text mode programs have a redisplay everything command, often associated with the Ctrl-L key combination.

Contents

Text mode video rendering came to prominence in the early 1970s, when video-oriented text terminals started to replace teleprinters in the interactive use of computers.

This section needs additional citations for verification. Please help improve this article by . Unsourced material may be challenged and removed.(December 2012) ()

The advantages of text modes as compared to graphics modes include lower memory consumption and faster screen manipulation. At the time text terminals were beginning to replace teleprinters in the 1970s, the extremely high cost of random access memory in that period made it exorbitantly expensive to install enough memory for a computer to simultaneously store the current value of every pixel on a screen, to form what would now be called a framebuffer. Early framebuffers were standalone devices which cost thousands of dollars, in addition to the expense of the advanced high-resolution displays to which they were connected. For applications that required simple line graphics but for which the expense of a framebuffer could not be justified, vector displays were a popular workaround. But there were many computer applications (e.g., data entry into a database) for which all that was required was the ability to render ordinary text in a quick and cost-effective fashion to a cathode ray tube.

Text mode avoids the problem of expensive memory by having dedicated display hardware re-render each line of text from characters into pixels with each scan of the screen by the cathode ray. In turn, the display hardware needs only enough memory to store the pixels equivalent to one line of text (or even less) at a time. Thus, the computer's screen buffer only stores and knows about the underlying text characters (hence the name "text mode") and the only location where the actual pixels representing those characters exist as a single unified image is the screen itself, as viewed by the user (thanks to the phenomenon of persistence of vision).

For example, a screen buffer sufficient to hold a standard grid of 80 by 25 characters requires at least 2,000 bytes. Assuming a monochrome display, 8 bits per byte, and a standard size of 8 times 8 bits for each character, a framebuffer large enough to hold every pixel on the resulting screen would require at least 128,000 bits, 16,000 bytes, or just under 16 kilobytes. By the standards of modern computers, these may seem like trivial amounts of memory, but to put them in context, the original Apple II was released in 1977 with only four kilobytes of memory and a price of $1,300 in U.S. dollars (at a time when the minimum wage in the United States was only $2.30 per hour). Furthermore, from a business perspective, the business case for text terminals made no sense unless they could be produced and operated more cheaply than the paper-hungry teleprinters they were supposed to replace.

Another advantage of text mode is that it has relatively low bandwidth requirements in remote terminal use. Thus, a text mode remote terminal can necessarily update the screen much faster than a graphics mode remote terminal linked to the same amount of bandwidth (and in turn will seem more responsive), since the remote server may only need to transmit a few dozen bytes for each screen update in text mode, as opposed to complex raster graphics remote procedure calls that may require the transmission and rendering of entire bitmaps.

Norton Utilities 6.01, an example of advanced TUI which redefines the character set to show tiny graphical widgets, icons and an arrow pointer in text mode.

The border between text mode and graphical programs can sometimes be fuzzy, especially on the PC's VGA hardware, because many later text mode programs tried to push the model to the extreme by playing with the video controller. For example, they redefined the character set in order to create custom semi-graphical characters, or even created the appearance of a graphical mouse pointer by redefining the appearance of the characters over which the mouse pointer was shown at a given time.

Text mode rendering with user-defined characters has also been useful for 2D computer and video games because the game screen can be manipulated much faster than with pixel-oriented rendering.

A video controller implementing a text mode usually uses two distinct areas of memory. Character memory or a pattern table contains a raster font in use, where each character is represented by a dot matrix (a matrix of bits), so the character memory could be considered as a three-dimensional bit array. Display matrix (a text buffer, screen buffer, or nametable) tracks which character is in each cell. In the simple case the display matrix can be just a matrix of code points (so named character pointer table), but it usually stores for each character position not only a code, but also attributes.

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A sample of character box and corresponding electronic scheme. The glyph is 8×8 pixels, with 3-bit low parts of scan line and dot counter. The screen is between 20×18 and 32×32 character cells, with 5-bit indices.

In the case of raster scan output, which is the most common for computer monitors, the corresponding video signal is made by the character generator, a special electronic unit similar to devices with the same name used in video technology. The video controller has two registers: scan line counter and dot counter, serving as coordinates in the screen dot matrix. Each of them must be divided by corresponding glyph size to obtain an index in the display matrix; the remainder is an index in glyph matrix. If glyph size equals to 2n, then it is possible just to use n low bits of a binary register as an index in glyph matrix, and the rest of bits as an index in the display matrix — see the scheme.

The character memory resides in a read-only memory in some systems. Other systems allow the use of RAM for this purpose, making it possible to redefine the typeface and even the character set for application-specific purposes. The use of RAM-based characters also facilitates some special techniques, such as the implementation of a pixel-graphics frame buffer by reserving some characters for a bitmap and writing pixels directly to their corresponding character memory. In some historical graphics chips, including the TMS9918, the MOS Technology VIC, and the Game Boy graphics hardware, this was actually the canonical way of doing pixel graphics.

Text modes often assign attributes to the displayed characters. For example, the VT100 terminal allows each character to be underlined, brightened, blinking or inverse. Color-supporting devices usually allow the color of each character, and often the background color as well, to be selected from a limited palette of colors. These attributes can either coexist with the character indices or use a different memory area called color memory or attribute memory.

Some text mode implementations also have the concept of line attributes. For example, the VT100-compatible line of text terminals supports the doubling of the width and height of the characters on individual text lines.

Depending on the graphics adapter used, a variety of text modes are available on IBM PC compatible computers. They are listed on the table below:

Text res. Char. size Graphics res. Colors Adapters
80×25 9×14 720×350 B&W Text MDA, Hercules
40×25 8×8 320×200 16 colors CGA, EGA
80×25 8×8 640×200 16 colors CGA, EGA
80×25 8×14 640×350 16 colors EGA
80×43 8×8 640×350 16 colors EGA
80×25 9×16 720×400 16 colors VGA
80×30 8×16 640×480 16 colors VGA
80×50 9×8 720×400 16 colors VGA
80×60 16 colors VESA-compatible Super VGA
132×25 16 colors VESA-compatible Super VGA
132×43 16 colors VESA-compatible Super VGA
132×50 16 colors VESA-compatible Super VGA
132×60 16 colors VESA-compatible Super VGA

MDA text could be emphasized with bright, underline, reverse and blinking attributes.

Video cards in general are backward compatible, i.e. EGA supports all MDA and CGA modes, VGA supports MDA, CGA and EGA modes.

By far the most common text mode used in DOS environments, and initial Windows consoles, is the default 80 columns by 25 rows, or 80×25, with 16 colors. This mode was available on practically all IBM and compatible personal computers. Several programs, such as terminal emulators, used only 80×24 for the main display and reserved the bottom row for a status bar.

Two other VGA text modes, 80×43 and 80×50, exist but were very rarely used. The 40-column text modes were never very popular outside games and other applications designed for compatibility with television monitors, and were used only for demonstration purposes or with very old hardware.

Character sizes and graphical resolutions for the extended VESA-compatible Super VGA text modes are manufacturer-dependent. Also on these display adapters, available colors can be halved from 16 to 8 when a second customized character set is employed (giving a total repertoire of 512 —instead the common 256— different graphic characters simultaneously displayed on the screen).

Some cards (e.g. S3) supported custom very large text modes, like 100×37 or even 160×120. In Linux systems, a program called SVGATextMode is often used with SVGA cards to set up very large console text modes, such as for use with split-screen terminal multiplexers.

Many modern programs with a graphical interface simulate the display style of text mode programs, notably when it is important to preserve the vertical alignment of text, e.g., during computer programming. There exist also software components to emulate text mode, such as terminal emulators or command line consoles. In Microsoft Windows, the Win32 console usually opens in emulated, graphical window mode. It can be switched to full screen, true text mode and vice versa by pressing the Alt and Enter keys together. This is no longer supported by the WDDM display drivers introduced with Windows Vista.

Linux virtual console operates in text mode. Most Linux distributions support several virtual console screens, accessed by pressing Ctrl, Alt and a function key together.

The AAlib open source library provides programs and routines that specialize in translating standard image and video files, such as PNG and WMV, and displaying them as a collection of ASCII characters. This enables a rudimentary viewing of graphics files on text mode systems, and on text mode web browsers such as Lynx.

Text mode Article Talk Language Watch Edit This article needs additional citations for verification Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed Find sources Text mode news newspapers books scholar JSTOR October 2010 Learn how and when to remove this template message 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 each of which contains one of the characters of a character set at the same time contrasted to all points addressable APA mode or other kinds of computer graphics modes Text mode applications communicate with the user by using command line interfaces and text user interfaces Many character sets used in text mode applications also contain a limited set of predefined semi graphical characters usable for drawing boxes and other rudimentary graphics which can be used to highlight the content or to simulate widget or control interface objects found in GUI programs A typical example is the IBM code page 437 character set An important characteristic of text mode programs is that they assume monospace fonts where every character has the same width on screen which allows them to easily maintain the vertical alignment when displaying semi graphical characters This was an analogy of early mechanical printers which had fixed pitch This way the output seen on the screen could be sent directly to the printer maintaining the same format Depending on the environment the screen buffer can be directly addressable Programs that display output on remote video terminals must issue special control sequences to manipulate the screen buffer The most popular standards for such control sequences are ANSI and VT100 Programs accessing the screen buffer through control sequences may lose synchronization with the actual display so that many text mode programs have a redisplay everything command often associated with the Ctrl L key combination Contents 1 History 2 Benefits 3 User defined characters 4 Technical basis 5 PC common text modes 6 Modern usage 7 See also 8 References 9 External links 10 Further readingHistory EditText mode video rendering came to prominence in the early 1970s when video oriented text terminals started to replace teleprinters in the interactive use of computers Benefits EditThis section needs additional citations for verification Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed December 2012 Learn how and when to remove this template message The advantages of text modes as compared to graphics modes include lower memory consumption and faster screen manipulation 1 At the time text terminals were beginning to replace teleprinters in the 1970s the extremely high cost of random access memory in that period made it exorbitantly expensive to install enough memory for a computer to simultaneously store the current value of every pixel on a screen to form what would now be called a framebuffer Early framebuffers were standalone devices which cost thousands of dollars in addition to the expense of the advanced high resolution displays to which they were connected For applications that required simple line graphics but for which the expense of a framebuffer could not be justified vector displays were a popular workaround But there were many computer applications e g data entry into a database for which all that was required was the ability to render ordinary text in a quick and cost effective fashion to a cathode ray tube Text mode avoids the problem of expensive memory by having dedicated display hardware re render each line of text from characters into pixels with each scan of the screen by the cathode ray In turn the display hardware needs only enough memory to store the pixels equivalent to one line of text or even less at a time Thus the computer s screen buffer only stores and knows about the underlying text characters hence the name text mode and the only location where the actual pixels representing those characters exist as a single unified image is the screen itself as viewed by the user thanks to the phenomenon of persistence of vision For example a screen buffer sufficient to hold a standard grid of 80 by 25 characters requires at least 2 000 bytes 1 Assuming a monochrome display 8 bits per byte and a standard size of 8 times 8 bits for each character a framebuffer large enough to hold every pixel on the resulting screen would require at least 128 000 bits 16 000 bytes or just under 16 kilobytes By the standards of modern computers these may seem like trivial amounts of memory but to put them in context the original Apple II was released in 1977 with only four kilobytes of memory and a price of 1 300 in U S dollars at a time when the minimum wage in the United States was only 2 30 per hour Furthermore from a business perspective the business case for text terminals made no sense unless they could be produced and operated more cheaply than the paper hungry teleprinters they were supposed to replace Another advantage of text mode is that it has relatively low bandwidth requirements in remote terminal use Thus a text mode remote terminal can necessarily update the screen much faster than a graphics mode remote terminal linked to the same amount of bandwidth and in turn will seem more responsive since the remote server may only need to transmit a few dozen bytes for each screen update in text mode as opposed to complex raster graphics remote procedure calls that may require the transmission and rendering of entire bitmaps User defined characters Edit Norton Utilities 6 01 an example of advanced TUI which redefines the character set to show tiny graphical widgets icons and an arrow pointer in text mode The border between text mode and graphical programs can sometimes be fuzzy especially on the PC s VGA hardware because many later text mode programs tried to push the model to the extreme by playing with the video controller For example they redefined the character set in order to create custom semi graphical characters or even created the appearance of a graphical mouse pointer by redefining the appearance of the characters over which the mouse pointer was shown at a given time Text mode rendering with user defined characters has also been useful for 2D computer and video games because the game screen can be manipulated much faster than with pixel oriented rendering Technical basis EditA video controller implementing a text mode usually uses two distinct areas of memory Character memory or a pattern table contains a raster font in use where each character is represented by a dot matrix a matrix of bits so the character memory could be considered as a three dimensional bit array Display matrix a text buffer screen buffer or nametable tracks which character is in each cell In the simple case the display matrix can be just a matrix of code points so named character pointer table but it usually stores for each character position not only a code but also attributes L C 0 0 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 0 1 1 0 0 1 0 0 0 0 1 0 1 0 0 1 1 0 0 0 1 1 1 00000000 11111111 00001111 00110011 01010101 11 00 00 00 01 00000 00001 00010 00011 00100 00101 00110 00111 01000 01001 A sample of character box and corresponding electronic scheme The glyph is 8 8 pixels with 3 bit low parts of scan line and dot counter The screen is between 20 18 and 32 32 character cells with 5 bit indices In the case of raster scan output which is the most common for computer monitors the corresponding video signal is made by the character generator a special electronic unit similar to devices with the same name used in video technology The video controller has two registers scan line counter and dot counter serving as coordinates in the screen dot matrix Each of them must be divided by corresponding glyph size to obtain an index in the display matrix the remainder is an index in glyph matrix If glyph size equals to 2n then it is possible just to use n low bits of a binary register as an index in glyph matrix and the rest of bits as an index in the display matrix see the scheme The character memory resides in a read only memory in some systems Other systems allow the use of RAM for this purpose making it possible to redefine the typeface and even the character set for application specific purposes The use of RAM based characters also facilitates some special techniques such as the implementation of a pixel graphics frame buffer by reserving some characters for a bitmap and writing pixels directly to their corresponding character memory In some historical graphics chips including the TMS9918 the MOS Technology VIC and the Game Boy graphics hardware this was actually the canonical way of doing pixel graphics Text modes often assign attributes to the displayed characters For example the VT100 terminal allows each character to be underlined brightened blinking or inverse Color supporting devices usually allow the color of each character and often the background color as well to be selected from a limited palette of colors These attributes can either coexist with the character indices or use a different memory area called color memory or attribute memory 2 Some text mode implementations also have the concept of line attributes For example the VT100 compatible line of text terminals supports the doubling of the width and height of the characters on individual text lines PC common text modes EditMain article VGA compatible text mode Depending on the graphics adapter used a variety of text modes are available on IBM PC compatible computers They are listed on the table below 3 Text res Char size Graphics res Colors Adapters80 25 9 14 720 350 B amp W Text MDA Hercules40 25 8 8 320 200 16 colors CGA EGA80 25 8 8 640 200 16 colors CGA EGA80 25 8 14 640 350 16 colors EGA80 43 8 8 640 350 16 colors EGA80 25 9 16 720 400 16 colors VGA80 30 8 16 640 480 16 colors VGA80 50 9 8 720 400 16 colors VGA80 60 16 colors VESA compatible Super VGA132 25 16 colors VESA compatible Super VGA132 43 16 colors VESA compatible Super VGA132 50 16 colors VESA compatible Super VGA132 60 16 colors VESA compatible Super VGA MDA text could be emphasized with bright underline reverse and blinking attributes Video cards in general are backward compatible i e EGA supports all MDA and CGA modes VGA supports MDA CGA and EGA modes By far the most common text mode used in DOS environments and initial Windows consoles is the default 80 columns by 25 rows or 80 25 with 16 colors This mode was available on practically all IBM and compatible personal computers Several programs such as terminal emulators used only 80 24 for the main display and reserved the bottom row for a status bar Two other VGA text modes 80 43 and 80 50 exist but were very rarely used The 40 column text modes were never very popular outside games and other applications designed for compatibility with television monitors and were used only for demonstration purposes or with very old hardware Character sizes and graphical resolutions for the extended VESA compatible Super VGA text modes are manufacturer dependent Also on these display adapters available colors can be halved from 16 to 8 when a second customized character set is employed giving a total repertoire of 512 instead the common 256 different graphic characters simultaneously displayed on the screen Some cards e g S3 supported custom very large text modes like 100 37 or even 160 120 In Linux systems a program called SVGATextMode is often used with SVGA cards to set up very large console text modes such as for use with split screen terminal multiplexers Modern usage EditMany modern programs with a graphical interface simulate the display style of text mode programs notably when it is important to preserve the vertical alignment of text e g during computer programming There exist also software components to emulate text mode such as terminal emulators or command line consoles In Microsoft Windows the Win32 console usually opens in emulated graphical window mode It can be switched to full screen true text mode and vice versa by pressing the Alt and Enter keys together 4 This is no longer supported by the WDDM display drivers introduced with Windows Vista 5 Linux virtual console operates in text mode Most Linux distributions support several virtual console screens accessed by pressing Ctrl Alt and a function key together The AAlib open source library provides programs and routines that specialize in translating standard image and video files such as PNG and WMV and displaying them as a collection of ASCII characters This enables a rudimentary viewing of graphics files on text mode systems and on text mode web browsers such as Lynx See also EditText based user interface Teletext Text semigraphics ASCII art Twin Hardware code page VGA text mode VGA compatible text mode detailsReferences Edit a b Bosch Winn L July 1992 The Perfect PC PC Magazine 11 13 186 Retrieved 15 December 2015 Text mode layout and palette Text modes on Ralf Browns interrupt list Windows uses Alt Enter to make a terminal full screen Some 16 bit DOS based Programs and the Command Prompt will not run in full screen mode in Windows Vista and in Windows 7 External links EditHigh Resolution console on LinuxFurther reading EditSignetics MOS Silicon Gate 2500 Series Metal Gate 2000 2400 Series Data Book PDF Sunnyvale CA USA Signetics Corporation 1972 pp 65 72 Archived PDF from the original on 2016 06 18 Retrieved 2016 06 18 NB For example Signetics 2513 MOS ROM Retrieved from https en wikipedia org w index php title Text mode amp oldid 1065580033, wikipedia, wiki, book,

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