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An insight into Display Adapters

No matter what device you are working on, be it a desktop computer, a laptop, a tablet or a smart phone, all possess a display screen or monitor, whose primary purpose is to display text, images, video, etc. When you buy a device you are often concerned about its screen resolution, how may colors it supports, and how fast the device is capable of processing image display. Have you ever wondered what is the technology behind, that ensures smooth rendering of images on the display device, making it comfortable for you to work on the device?

This brings us to the topic of Display Adapters. A Display Adapter, also known as video card / video board / video display board / graphics card, is a card that plugs into a computer to give its display capabilities. It is a piece of hardware that is responsible for generating the images that appear on your visual display unit - the monitor.

The display capabilities of a computer depend upon two parts of the hardware:

  1. Video Adapter
  2. Monitor

The significant display properties are:

  1. Monochrome / Color support
  2. Text / Graphics support
  3. Resolution
  4. Specialized properties like graphics acceleration

Displaying high resolution images and millions of colors entail processing enormous amount of data. This demands a significant amount of processing power and computer memory. To appreciate this, let us look at an example of a basic screen resolution of 1024 x 768 pixels. This is very basic from today's standards. Now, 1024 x 768 pixels gives you a matrix of 786,432 pixels. If the screen uses a 32 bits/pixel color depth, which is pretty basic from today's standards, the memory required to store a single frame of data will be = 786,432 x 32 = 25,165,824 bits = 3 MB. And when we are rendering video, a typical screen may be displaying 100 - 200 frames per second. Imagine the gamut of processing required and hence the amount of resource required to handle the same. Hence, a display adapter, also known today as a graphics adapter is a must for every computing device. This is usually fitted in a computer system as an add-on card with its own graphic processing unit (GPU) and own dedicated memory of 4-64 GB. They are essentially a computer system within your main computer system and help free up your main CPU from the load of processing graphics.

In the early personal computers the display adapter was built in the form of an expansion card that was mounted in one of the ISA (Industry Standard Architecture) slots on the computer's motherboard. It used the Monochrome Display Adapter (MDA) standard and was only capable of displaying text at a screen resolution of 720 x 350 pixels.

Modern display adapters have taken the form of a separate card or are even integrated within the motherboard. They are designed to operate at very high resolutions and display millions of colors. The adapter capability have improved so much over time that even a basic display adapter today is capable of handling complex graphics processing such as computer animations, video playback and 3D games. This enhanced capability has helped in the fast development of the computer gaming industry as well.


Types of Video Display Adapters

Here is a summarized list of various types of display adapters, arranged in chronological order of their development.

Monochrome Display Adapter (MDA)

An old monochrome video standard for PCs. The monochrome display adapter (MDA) was the first display adapter available. It was introduced by IBM in 1981. MDA supports a resolution of 720 x 350 for monochrome text. It does not support graphics or color. It is designed to work with a monochrome transistor-transistor logic (TTL) monitor. It is a text-only system that cannot display graphics or color. The MDA uses a 9 x 14 dot character box that provides clean sharp characters. Because most of the software packages developed today, even word processing and spreadsheets, use graphics to some extent, the MDA is considered obsolete now.


Color Graphics Adapter (CGA)

The color graphics adapter (CGA) was, at one time, the most common graphics adapter available - the first color graphics system for IBM PCs. It supports an RGB monitor with a maximum resolution of 640 x 200 pixels and 2 colors. The CGA card has two modes of operation: alphanumeric (A/N) and all points addressable (APA). In both modes, the basic character set is formed with a resolution of 8 x 8 pixels. The CGA card displays either 40 or 80 columns with 25 lines of text. In the A/N mode, the CGA card can display up to 16 colors. The all points addressable mode of operation can address each pixel individually. The CGA APA mode supports two resolutions on the screen: medium and high. The medium resolution is capable of addressing 320 x 200 pixels with 4 colors. The high resolution is capable of a 640 x 200 display using 2 colors. Because of these limitations, the CGA adapter is generally considered obsolete now.


Hercules Graphics Adapter (HGA)

Developed by Van Suwannukul in 1982. An old graphics display system which produces high resolution (720 x 350 pixels) text and graphics for monochrome monitors.


Multicolor Graphics Array or Memory Controller Gate Array (MCGA)

The system was built into some older PCs. It provides graphics capabilities equal to or greater than MDA & CGA, but is not as powerful as EGA or VGA.


Enhanced Graphics Adapter (EGA)

The enhanced graphics adapter (EGA) superseded the CGA adapter and drives an RGB monitor. IBM introduced this in 1984. The EGA provides 16 colors at a resolution of 320 x 200 or 640 x 200. The character box for text is 8 x 14 instead of the 8 x 8 used with the CGA card. The EGA card comes with 64K of video memory that is expandable to 256K using a graphics memory expansion card. This card adds an additional 64K of video memory. The EGA card also uses 128K of RAM from the computer's RAM. The video is stored just above the 640K boundary. Video memory is used to refresh the display, freeing up the CPU chip for other operations.


Video Graphics Array (VGA)

Again developed by IBM in 1987 - a de-facto standard for PCs in those days. The video graphics array (VGA) adapter card overcame the limitations earlier adapters had in displaying high quality color. The earlier adapters used digital signals to control the three electron guns of the CRT. Each gun was either turned on or off by these signals and limited the display to 8 colors. By adding a high and a low intensity signal, the number of colors that could be displayed was doubled to 16. The VGA card generates analog signals to control the electron guns and, therefore, can control the intensity of each gun at varying levels.

In text mode, VGA provides 720x400 resolution; and in graphics mode it provides 640x480 with 16 colors & 320x200 with 256 colors.


8514/A

A high resolution video standard developed by IBM in 1987. Provides a resolution of 1024x768, which is 2.5 x VGA.


Super Video Graphics Adapter (SVGA)

Super video graphics array (SVGA) is a term used to describe graphic adapters that have exceeded those of the VGA system. This standard was developed by a consortium of monitors and graphics manufacturers called VESA (Video Electronics Standards Association). SVGA arrived in the late 1980s. Resolutions for SVGA vary by manufacturer but 800x600, 1024x768, 1280x1024, 1600x1200 are common. Some SVGA cards work on a 60-Hz vertical scan rate and some use 70 Hz. Once an SVGA card is installed, a software driver that describes the specifications of that card needs to be installed.


Extended Graphics Array (XGA)

A high resolution graphics standard introduced in 1990. It was designed to replace the older 8514/A video standard. It provides the same resolution as 8514/A but supports more colors.

The extended graphics array (XGA) is a refinement of the VGA standard. The XGA system provides a 32-bit bus master for micro channel-based systems. The bus master has its own processor that allows it to operate independently of the motherboard, freeing the main processor. The XGA system also provides greater resolution and more colors than the VGA system. The XGA can hold up to 1 MB of video memory. Resolution is variable, depending on the mode selected. Maximum resolution is 1024 x 768, with the capability of displaying 256 colors from a palette of 262,144 colors. The XGA can also display 65,536 colors at a resolution of 640 x 480, providing almost photographic quality color.


Current Display Adapter Standards

With increase in demand for high resolution graphics and a diverse range of user applications, several adapter standards have emerged now. The need for widescreen formats giving the capability to display two pages of a document side by side, and also to display widescreen movies have propelled the development of several newer enhanced adapter types, some of which are listed below.

Widescreen Extended Graphics Array (WXGA)

EXGA is an extension of XGA found on recent laptops. It provides pixel resolutions of 1280 x 800, 1366 x 768, and 1300 x 768. Depending upon the X & Y of the pixel resolutions, you get different screen aspect ratios. For example: 1280 x 800 gives an aspect ratio of 16:10 whereas 1366 x 768 gives an aspect ratio of 16:9. Pixel resolution of 1300 x 768 gives an aspect ratio of 17:10, which is a narrower aspect ratio and is often found in 26" LCD television screens.


Super XGA (SXGA)

SXGA is also referred as XVGA (Extended VGA). SXGA provides a screen resolution of 1280 x 1024 pixels (5:4 aspect ratio). This is commonly found in 17" and 19" LCD monitors.


Super XGA Plus (SXGA+)

SXGA+ is commonly found in 14" & 15" screens that are generally used in laptops/notebooks. SXGA+ provides a resolution of 1400 x 1050 at 4:3 aspect ratio.


Widescreen Extended Graphics Array Plus (WXGA+ or WSXGA)

WXGA+ a non-standard adapter technology that provides display resolution of 1440 x 900 pixels at 16:10 aspect ratio. It is commonly found in 19" widescreen LCD monitors.


Ultra XGA (UXGA)

The UXGA standard provides a resolution of 1600 x 1200 pixels at 4:3 aspect ratio of 4:3. This ia a native resolution for 20" & 23" LCD monitors.


Widescreen SXGA (WSXGA)

WSXGA provides screen resolution of 1680 x 1050 pixels at 16:10 aspect ratio, and is commonly found in 22" monitors.


Widescreen UXGA (WUXGA)

The WUXGA standard provides a resolution of 1920 x 1200 pixels at 16:10 aspect ratio. This adapter standard is used in high-end notebook computers and generally in 23" - 27" widescreen LCD monitors.


Quad Wide Extended Graphics Array (QWXGA)

The QWXGA adapters support 2048 x 1152 pixels screen resolution (aspect ratio = 16:9), and are found in 23" LCD monitors produced by Samsung and Dell.


Widescreen Quad Extended Graphics Array (WQXGA)

WQXGA supports 2560 x 1600 pixels at 16:10 aspect ratio. This adapter standard is used for 30" widescreen LCD monitors.




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About the Author

Rajeev Kumar
CEO, Computer Solutions
Jamshedpur, India

Rajeev Kumar is the primary author of How2Lab. He is a B.Tech. from IIT Kanpur with several years of experience in IT education and Software development. He has taught a wide spectrum of people including fresh young talents, students of XLRI, industry professionals, and govt. officials.

Rajeev has founded Computer Solutions & WebServicesWorldwide.com, and has hands-on experience of building variety of web applications and portals, that include - SAAS based ERP & e-commerce systems, independent B2B, B2C, Matrimonial & Job portals, and many more.



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