f2 X icon 3 y2 steam2
 Search find 4120

Overview of Graphics Cards

A video card (also known as a graphics card, graphics card, video adapter) (English videocard) is a device that converts an image stored in computer memory into a video signal for a monitor. Usually, a video card is an expansion card and is inserted into the expansion slot, universal (PCI-Express , PCI, ISA, VLB) or specialized (AGP), but it can also be built-in (integrated) into the system board. Modern video cards are not limited to simple image output, they have an integrated graphics microprocessor that can perform additional processing, offloading the central processor from these tasks computer. For example, all modern NVIDIA and AMD (ATi) graphics cards support OpenGL applications at the hardware level.


One of the first graphics adapters for the IBM PC was the MDA (Monochrome Display Adapter) in 1981. It only worked in text mode with a resolution of 80x25 characters (physically 720x350 pixels) and supported five text attributes: normal, bright, inverted, underlined, and blinking. It could not transmit any color or graphic information, and the color of the letters was determined by the model of the monitor used. Usually they were black and white, amber or emerald. In 1982, Hercules released a further development of the MDA adapter, the HGC video adapter (Hercules Graphics Controller - Hercules graphics adapter), which had a graphics resolution of 720 × 348 pixels and supported two graphics pages. But he still didn't let me work with color.

The first color video card was the CGA (Color Graphics Adapter), released by IBM and which became the basis for subsequent video card standards. It could work either in text mode with resolutions of 40x25 and 80x25 (character matrix - 8x8), or in graphics mode with resolutions of 320x200 or 640x200. In text modes, 256 character attributes are available - 16 character colors and 16 background colors (or 8 background colors and a blink attribute), in 320x200 graphics mode, four palettes of four colors each were available, and 640x200 high-resolution mode was monochrome. In the development of this card, EGA (Enhanced Graphics Adapter) appeared - an improved graphics adapter with an expanded palette of up to 64 colors and an intermediate buffer. The resolution has been improved to 640x350, resulting in 80x43 text mode with an 8x8 character matrix. For the 80×25 mode, a large matrix was used - 8×14, 16 colors could be used simultaneously, the color palette was expanded to 64 colors. The graphics mode also allowed using 16 colors from a palette of 64 colors at a resolution of 640 × 350. Was compatible with CGA and MDA.

It is worth noting that the interfaces with the monitor of all these types of video adapters were digital, MDA and HGC transmitted only the dot is lit or not lit and an additional brightness signal for the “bright” text attribute, similarly CGA transmitted the main video signal on three channels (red, green, blue) , and could additionally transmit a luminance signal (16 colors in total), EGA had two transmission lines for each of the primary colors, that is, each primary color could be displayed at full brightness, 2/3, or 1/3 of full brightness, which and gave a total of a maximum of 64 colors.

In early models of computers from IBM PS / 2, a new graphics adapter MCGA (Multicolor Graphics Adapter - multi-color graphics adapter) appears. The text resolution was raised to 640x400, which allowed using the 80x50 mode with an 8x8 matrix, and using an 8x16 matrix for the 80x25 mode. The number of colors was increased to 262144 (64 brightness levels for each color), for compatibility with EGA in text modes, a color table was introduced, through which the 64-color EGA space was converted to the MCGA color space. A 320x200x256 mode appeared, where each pixel on the screen was encoded by the corresponding byte in the video memory, there were no bit planes, respectively, only text modes remained compatible with EGA, compatibility with CGA was complete.

Then IBM went a step further and made VGA (Video Graphics Array), an EGA-compatible MCGA extension introduced in the mid-range PS/2 models. This is the de facto video adapter standard since the late 80s. Added 720x400 text resolution for MDA emulation and 640x480 graphics mode, accessed via bitplanes. The 640x480 mode is remarkable in that it uses a square pixel, that is, the ratio of the number of pixels horizontally and vertically coincides with the standard aspect ratio of the screen - 4:3. Then came the IBM 8514/a with 640x480x256 and 1024x768x256 resolutions, and the IBM XGA with 132x25 text mode (1056x400) and increased color depth (640x480x65K).

Since 1991, the concept of SVGA (Super VGA - “over” VGA) has appeared - an extension of VGA with the addition of higher modes and additional services, such as the ability to set an arbitrary frame rate. The number of simultaneously displayed colors increases to 65'536 (High Color, 16 bit) and 16'777'216 (True Color, 24 bit), additional text modes appear. From the service functions, support for VBE (VESA BIOS Extention - an extension of the VESA standard BIOS) appears. SVGA has been perceived as the de facto video adapter standard since mid-1992, after the adoption of the VBE version 1.0 standard by the Video Electronics Standard Association (VESA). Until that moment, almost all SVGA video adapters were incompatible with each other.

The graphical user interface, which appeared in many operating systems, stimulated a new stage in the development of video adapters. The concept of "graphics accelerator" (graphics accelerator) appears. These are video adapters that perform some graphics functions at the hardware level. These functions include moving large image blocks from one screen area to another (for example, when moving a window), filling image areas, drawing lines, arcs, fonts, supporting a hardware cursor, etc. A direct impetus to the development of such a specialized device was the fact that the graphical user interface is undoubtedly convenient, but its use requires considerable computing resources from the central processor,


Device A
modern video card consists of the following parts:
GPU(Graphics processing unit - graphic processing unit) - deals with calculations of the displayed image, freeing the central processor from this responsibility, performs calculations for processing 3D graphics commands. It is the basis of the graphics card, it is on it that the speed and capabilities of the entire device depend. Modern graphics processors are not much inferior in complexity to the central processing unit of a computer, and often surpass it both in the number of transistors and in computing power, thanks to a large number of universal computing units. However, the previous generation GPU architecture usually assumes the presence of several information processing units, namely: a 2D graphics processing unit, a 3D graphics processing unit, in turn,
Video controller - is responsible for the formation of the image in the video memory, gives RAMDAC commands to generate scan signals for the monitor and processes requests from the central processor. In addition, there is usually an external data bus controller (for example, PCI or AGP), an internal data bus controller, and a video memory controller. The width of the internal bus and the video memory bus is usually larger than the external one (64, 128 or 256 bits versus 16 or 32), RAMDAC is also built into many video controllers. Modern graphics adapters (ATI, nVidia) usually have at least two video controllers that work independently of each other and control one or more displays at the same time each.
video memory- acts as a frame buffer, which stores an image generated and constantly modified by the graphics processor and displayed on the monitor (or multiple monitors). The video memory also stores intermediate elements of the image that are invisible on the screen and other data. There are several types of video memory, differing in access speed and operating frequency. Modern video cards are equipped with DDR, DDR2, GDDR3, GDDR4 and GDDR5 memory types. It should also be borne in mind that in addition to the video memory located on the video card, modern graphics processors usually use in their work a part of the total system memory of the computer, direct access to which is organized by the video adapter driver via the AGP or PCIE bus.
D/A Converter(DAC, RAMDAC - Random Access Memory Digital-to-Analog Converter) - is used to convert the image generated by the video controller into color intensity levels supplied to an analog monitor. The possible color range of the image is determined only by the RAMDAC parameters. Most often, RAMDAC has four main blocks - three digital-to-analog converters, one for each color channel (red, green, blue, RGB), and SRAM for storing gamma correction data. Most DACs have a bit depth of 8 bits per channel - it turns out 256 brightness levels for each primary color, which gives a total of 16.7 million colors (and due to gamma correction, it is possible to display the original 16.7 million colors in a much larger color space) . Some RAMDACs have 10 bits per channel (1024 brightness levels), which allows you to immediately display more than 1 billion colors, but this feature is practically not used. To support a second monitor, a second DAC is often installed. It should be noted that monitors and video projectors connected to the digital DVI output of the video card use their own digital-to-analog converters to convert the digital data stream and do not depend on the characteristics of the DAC of the video card.
Video ROM (Video ROM) is a read-only memory device that contains video BIOS, screen fonts, service tables, etc. ROM is not used directly by the video controller - only the central processor accesses it. The video BIOS stored in ROM ensures the initialization and operation of the video card before the main operating system is loaded, and also contains system data that can be read and interpreted by the video driver during operation (depending on the method of division of responsibility between the driver and the BIOS). On many modern cards, electrically reprogrammable ROMs (EEPROM, Flash ROM) are installed that allow the user to overwrite the video BIOS by the user using a special program.
Cooling system- designed to keep the temperature of the video processor and video memory within acceptable limits.

The correct and fully functional operation of a modern graphics adapter is ensured using a video driver - special software supplied by the manufacturer of the video card and loaded during the startup of the operating system. The video driver acts as an interface between the system running applications on it and the video adapter. Just like the video BIOS, the video driver organizes and programmatically controls the operation of all parts of the video adapter through special control registers, which are accessed through the corresponding bus.