CompTIA A+ Certification

The monitor is half of a computer's display system and must be matched to a display adapter card, although some entry level motherboards have integrated display adapters built into the motherboard's circuitry. The display adapter has gone through several major evolutions as the nature of computers changed.

Display Adapter (MDA):
The early 8088-based IBM personal computers used Monochrome Display Adapter (MDA) cards which were matched to the limited capabilities of the early monitors. The MDA offered a simple textbased monochrome display, producing an 80-character-wide row of text at a resolution of 720 × 350 pixels. The MDA card was a 1-bit device, with each pixel using 1 bit, valued either 0 or 1 to represent whether a given pixel was on or off. It was equipped with 256 KB of dynamic RAM (DRAM) but relied on the CPU to process the display image. It also had a 9-pin d-shell, male connector to which the monitor cable was attached.

Color Graphics Adapter(CGA):
The MDA was superseded by the Color/Graphics Adapter (CGA) card which provided up to four colors: amber, green, white and black. These colors were in fact different intensities of the monitor's active color. In four-color mode, CGA provided a resolution of 320 × 200 pixels and a resolution of 640 × 200 pixels in two-color mode. Like the MDA, the CGA had 256KB of DRAM but relied on the CPU to process the display and had a 9-pin d-shell, male connector to attach the monitor cable.

Enhanced Graphics Adapter (EGA):
The Enhanced Graphics Adapter (EGA) card was an improved version of CGA card and was the first display adapter card that gave the computer the capability to use actual color. The EGA used the same 9-pin d-shell, male connector that was used by the MDA and CGA to attach the monitor cable and had a maximum resolution of 640 × 350 with 16 colors in text-only mode, and a resolution of 640 × 200 with two colors in graphics mode. However, the EGA was not fully backward-compatible with CGA and MDA.

Professional Graphics Adapter (PGA):
Graphic artists, engineering designers, and the manipulation of photo-realistic images needed more the 16-color display provided by the EG A. In response to this need, IBM offered a short-lived and very complicated engineering display adapter, the Professional Graphics Adapter (PGA). It required three ISA slots, and provided limited three-dimensional manipulation and 60-frames-per-second animation of a series of images. It was, however, very expensive.

Video Graphics Array (VGA):
One reason for the demise of the PGA was the advent of the Video Graphics Array (VGA). All the preceding cards were digital devices, but the VGA produced an analog signal. That required new cards, new monitors, and a 15-pin female connector. Developers were then able to produce cards that provided the user with up to 262,144 colors and resolutions up to 640 × 480. The VGA card quickly became commonplace for a computer display system.
Note: The VGA has a maximum resolution of 640 × 480. This resolution is used when VGA mode is used.

Super VGA (SVGA):
Thereafter the Video Electronics Standard Association (VESA) developed a standard list of display modes that extended VGA to the high-resolution color and photographic quality we know today. This standard is known as Super VGA (SVGA). The SVGA set specifications for resolution, refresh rates, and color depth for compatible adapters. On Pentium and later computers, an SVGA adapter is the minimum standard for display systems. The lowest resolution needed for SVGA compatibility is 640 × 480 with 256 colors, and most modern adapters usually go far beyond that. The other standard SVGA resolutions are 800 × 600 and 1024 × 768. High-end systems with large monitors are sold at 1600 × 1200 resolution at high refresh rates.
The SVGA specification for 256 shades of gray is one of the basic SVGA specifications for true photographic reproduction of monochrome images; it is the number of shades that the human eye can distinguish in a grayscale photo. Color requires the same number of shades for each color in the image to achieve the same level of visual realism. To get 256 shades requires an 8-bit memory address system inside the card. However, an 8-bit display adapter card cannot display all the colors of a full-color picture in color mode, therefore a lookup table is used to figure the closest match to a hue that cannot be represented directly. This method kept the cost of the early SVGA cards low.
With the advent of the 80486 processor, 16-bit SVGA cards, which allowed approximately 64,000 colors, were developed. More bits require more memory, more processing requirements, a larger lookup table, and a higher cost. These cards were designed to be used with larger monitors, 15 to 17 inches at 800 × 600 or 1024 × 768 resolution. The new systems were too expensive for average users, but graphics professionals and power users generated a large enough market to fuel development.

Extended Graphics Array (XGA):
In 1991 IBM introduced the Extended Graphics Array (XGA). The XGA was only available as an Micro Channel Architecture (MCA) expansion card. The MCA expansion slot was an IBM propriety expansion slot that IBM developed for their PS/2 computers. The XGA could support 256 colors at 1,024 × 768 pixels or 65,536 colors at 640 × 480 pixels. Its design was optimized for graphical user interfaces (GUIs) such as Microsoft Windows or OS/2, and used interlaced technology. Because the MCA expansion slot was an propriety expansion slot only used on IBM computers, XGA display adapter cards are rare. Most of the early SVGA card used the PCI expansion bus, however, having more cards on a single bus slowed down the performance of these display adapter cards, just when 24-bit display adapters and 3D rendering called for greater demands on the display system. This led Intel to developed the Accelerated Graphics Port (AGP), a single slot tuned for the display adapter. The AGP removes all the display data traffic from the PCI bus and gives that traffic its own 525-MB-per-second pipe into the system's chip set and, from there, straight to the CPU. It also provides a direct path to the system memory for handling graphics.