What is VGA (Video Graphics Array)?

Video Graphics Array, or VGA, is a common type of computer screen. For instance, IBM first made this type in 1988. It also has a special small plug, called a 15-pin D-sub.

The VGA type can show 640×480 dots and has a 4:3 screen shape. This was a huge change back then. For one, it could show 256 colors at once, giving a big range of colors. In the end, it created a new mark for how good pictures look.

VGA has become a fundamental and vital technology over time. It has also shaped the screen types that came after it. Its 15-pin plug is now a famous symbol, making it a regular part of computer pictures.

Even though digital video is now common, VGA is still a key part. So, it is still used in many ways right now.

What is a VGA Connector?

VGA was the last graphics standard offered by IBM, and most PC manufacturers followed suit. Thus, VGA became the minimum supported by all graphics hardware.

For example, when the system is running in VGA mode, the Microsoft Windows screen appears. This results in a lower resolution and limited color depth.

Officially, IBM’s XGA standard replaced VGA. However, extensions developed by various manufacturers became known as Super VGA.

Historical

In 1987, IBM introduced the display hardware known as VGA. This system was installed in the IBM PS/2 series of computers.

While the PC series achieved limited success, VGA spread rapidly. As a result, it became a universal standard for many manufacturers.

VGA stands for Video Graphics Array. However, because most adapters were compatible, it became known as a Video Graphics Adapter.

While still used in many computers, newer versions emerged, and VGA became an increasingly uncommon technology.

It was officially replaced by IBM’s XGA standard. However, other companies began producing their own versions. Therefore, the standard evolved before IBM released its own version.

VGA Connector

The VGA connector is known as the DE-15, a three-row, 15-pin connector. There are also four different versions.

The original, DDC2, the oldest, and Mini-VGA versions are available. Most video cards and monitors have a 15-pin connector. This common connector is almost always known as HD-15.

HD distinguishes it from similar two-row connectors. However, it is often incorrectly called DB-15 or HDB-15. VGA connectors carry DDC2 clock and data signals.

They are also used to transmit analog RGBHV components. A Mini-VGA port may be preferred when size is limited.

What are the Features of the VGA Port?

Since its implementation as a single chip, EGA was preferred from the outset. Furthermore, EGA replaced the Motorola 6845, MDA, CGA, and ISA cards.

For this reason, it was called an “Array” rather than an adapter. However, the EGA easily plugs directly into a PC motherboard.

The first IBM PS/2 models were equipped with a VGA interface on the motherboard. Finally, the VGA specifications are as follows:

• 256 KB Video RAM
• Modes: 16 colors and 256 colors
• 262144 color palette values ​​(6 bits for red, green, and blue)
• Selectable 25.2 MHz or 28.3 central clock
• 720 horizontal pixels maximum
• 480 lines maximum
• Refresh rate up to 70 Hz
• Blank vertical cut (Not all cards support)
• Flat mode: maximum of 16 colors
• Packed pixel mode: 256-color mode (13-hour mode)
• Scroll stand
• Some bitmap operations
• Barrel changer
• Support split screen
• 0.7 V peak-to-peak
• 75-ohm impedance (9.3mA – 6.5mW)

It supports all addressable point modes and alphanumeric text modes. Standard graphics modes:

• 640×480 in 16 colors
• 640×350 in 16 colors
• 320×200 in 16 colors
• 320×200 in 256 colors

Besides the standard modes, it can be configured to emulate any of its previous modes (EGA, CGA, and MDA).

Standard Text Modes

Standard text modes use 80×25 or 40×25 cells. Each cell can select one of 16 foreground colors.

In addition, one of 8 background colors can be selected. Up to 8 background colors are allowed without High-Density Bit. Furthermore, flashing characters flash together.

The interlaced option for the entire screen can change the background color. These options are the same as IBM’s CGA adapter.

Adapters generally support both black and white and color modes. However, Monochrome mode is rarely used. Almost all modern adapters offer gray text with a black background.

Monochrome monitors were primarily sold for text applications. However, most work with VGA adapters in color mode. Sometimes, a faulty connection causes the card to perceive the monitor as monochrome.

This is why the BIOS and boot process appear in grayscale. The monitor usually returns to color after the graphics card drivers are installed.

In color text mode, each character is represented by two bytes. The smallest character set represents the actual character.

The top byte is used to select color, dithering, and character set. This byte-matching scheme is one of the features VGA inherited from CGA.

Color Palette

The VGA color system is compatible with EGA and CGA adapters. It also adds an additional level of configuration. CGA can display up to 16 colors. However, EGA allows each color to be selected from a palette of 64.

VGA expands the EGA palette from 64 to 256 inputs. Black has 8 free inputs. Furthermore, more than 64 colors are added with progressive darker tones. In addition to expanding the palette, the 256 inputs can be randomly assigned colors via the DAC.

The EGA BIOS represents only 2 bits per channel. However, VGA represents the intensity of red, green, and blue with 6 bits. This provides a total of 63 different intensity levels. This results in 262,144 possible colors and 256 assignable colors. In fact, this method combines the palette systems in EGA and CGA graphics modes.

For example, in text mode, red text should be set to one of the CGA colors. This color is then individually mapped to the EGA palette. CGA color 7 is mapped to EGA input 42. The VGA DAC should set color 42 to dark red. This means everything seen in gray light is dark red. This is often used in 256-color DOS games.

Supported CGA and EGA modes display 16 colors simultaneously. Furthermore, VGA modes, such as 13-clock mode, display 256 palette inputs. This means that 256 colors out of the 262,144 available colors appear on the screen.

Address İnfo

VGA Video memory is mapped to PC memory through a window between the 0xA000 and 0xC000 segments in the real-mode address space. Usually, these segments are:

1. 0xA000 (64 KB) for EGA/VGA graphics modes
2. 0xB000 (32 KB) for monochrome in text mode
3. 0xB800 CGA modes supported for text mode color and graphics (32 KB)

Different modes use different addresses. This allows two adapters to be installed in the same machine. Compatible with monochrome displays and VGA, EGA, or CGA.

This method was used in the early 1980s. For example, an MDA displayed high-resolution Lotus 1-2-3 charts on a monitor, while a CGA displayed lower-resolution graphics.

Many programmers use this feature for debugging. For example, information can be displayed while the other card is running in graphics mode.

Tools such as Borland Turbo Debugger, D86, and CodeView work on dual monitors. Turbo Debugger or CodeView can also be used in Windows.

DOS device drivers are also available. For example, ox.sys simulates a serial interface, allowing the user to receive error messages without using a physical terminal.

It is possible to redirect output to a monochrome display. The “MONO MODE” command can be used at the DOS Command Prompt.

If a monochrome display is not available, addresses 0xB000–0xB7FF can be used. This area is also suitable for programs loaded into high memory.

VGA Programming

An undocumented but popular technique nicknamed Mode X (created by Michael Abrash) was used to enable programming techniques and graphics resolutions that were not in the Mode 13h standard.

This was done by splitting the 256 KB of VGA memory into four planes, which would make all 256 KB of VGA RAM available in 256-color color modes. There was extra compensation for the complexity and performance loss in some graphics operations, but in some cases, it was reduced by other operations more quickly:

• Filling polygons with one color can be speeded up due to the ability to set four Pixels with a single write to the hardware.
• The video adapter can help copy video RAM zones, which is sometimes faster than doing it with a slow CPU and VGA interface.

Several high-resolution modes are possible, for example, up to 704×528 and 800×600 in 16 colors. Software like ColoRIX also supports 256-color modes.

These include combinations of 256, 320, and 360 columns and 200–480 rows. However, 320×240 is the most widely known and used mode because it is the typical 4:3 image format with a square pixel resolution.

It is possible to use multiple video feeds in hardware, allowing the developer to double buffer in all 16-color VGA modes. However, using the 13-clock mode was not possible.

Sometimes, the monitor refresh rate must be reduced. This can also increase eye strain and cause display problems.

Missing detail, flickering, scrolling, and lack of synchronization are common on some older monitors.

Therefore, VGA settings are limited in commercial products. For example, 320×240, 320×400, and 360×480 are safe combinations.