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- Generalities


- Small history of the videocards

- The resolution and the number of colors

- The refreshment speed

- Video memory

- Connectors: PCI, AGP...

- Adequacy to the use of the computer

Updated page
10/25/1999


Author:
Juan Herrerías Rey
 

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What is... the videocard?


 

In an abridged way, this is what transmits to the monitor the graphic information that it must present on the screen. With something more about detail, it realizes two operations:

  • He interprets the information that come to him from the processor, arranging them and calculating to be able to present them on the screen in the shape of a more or less big rectangle consisted of individual points of different colors (pixels).
  • It takes the exit of digital information resultant from this process and transforms it into an analogical sign that could understand the monitor.

These two processes are usually realized by one or more chips: the graphic microprocessor (the brain of the graphic card) and the analogical - digital converter or RAMDAC, although sometimes accessories exist chips for other functions or they they all are realized by the only chip.

The microprocessor can be very powerful and advanced, so much or more than the own mike of the computer; that's why they have some up to proper name: Virge, Rage Pro, Voodoo, TNT2... Even them there is with architectures of 256 bits, the fourfold one that the Pentium.

 

Small history of the videocards

In the beginning, the computers were blind; all the earnings and exits of information were realized by means of perforated cards of information, or by means of the keyboard and primitive printers. A good day, someone thought that it was much more comfortable to connect a TV set species to the computer to observe the evolution of the process and the information, and there arose the monitors, which had to receive his information of certain specializing hardware: the videocard.

MDA

In the first computers, the graphs were shining... for his absence. The first videocards were presenting only monochrome text, generally in an agreeable tone amber or green fosforito that was leaving the made eyes dust concerning minutes. Hence they were named MDA, Monochrome Display Adapter.

CGA

Then, with the arrival of the first PCs, there arose a videocard capable of presenting graphs: the CGA (Computer Graphics Array, graphic device for computers). So exciting invention was capable of presenting graphs of several ways:

CGA

Resolution (horizontal x vertical)

Colors

320x200

4

640x200

(Monochrome) 2

Which, although it seems incredible, turned out to be the whole revolution. There appeared multitude of games that were making use to the maximum of so meager possibilities, in addition to more serious programs, and the graphs settled forever in the PC.

Hércules

This one was talking each other of a graphic card of deeply professional court. His advantage, to be able to work with graphs to 720x348 resolution points, something amazing for the epoch; his disadvantage, which was not offering color. It is for this lack over which it did not spread any more, because to play without color is not the same, and the world PC advances of the hand of the designers of games (and it goes very seriously).

EGA

Another successful IBM inventito. A capable card of:

EGA

Resolution (horizontal x vertical)

Colors

320x200

16

640x200

16

640x350

16

These numbers were making already possible that the graphic environments were extending to the world PC (the Apple were taking years with it), and they appeared the GEM, the Windows and many others. On the possibilities of the screens EGA, a curiosity: the drivers EGA of Windows 3.1 work on Windows 95, and it turns out to be curious (and extremely uncomfortable, the truth) to see the above mentioned combination...

VGA

The standard, the screen of use forced for already 10 years. It has multitude of possible ways of video, although the most common is of 640x480 points with 256 colors, known generally like "standard VGA" or "resolution VGA".

SVGA, XGA and Superiors

The success of the VGA led numerous companies to creating its own enlargement of the same one, always centring on increasing the resolution and/or the number of available colors. Between they were:

Video way

Maximum resolution and maximum number of colors

SVGA

800x600 and 256 colors

XGA

1024x768 and 65.536 colors

IBM 8514/TO

1024x768 and 256 colors (it does not allow 800x600)

Anyway, the border between a few standards and others is extremely confused, since most of the cards are compatible with more than one standard, or with some of his ways. Also, some cards offer additional ways on having added more video memory.

 

The resolution and the number of colors

In the context that occupies us, the resolution is the number of points that is capable of presenting for screen a videocard, so much in horizontal as in vertical. This way, "800x600" it means that the image each one is formed by 600 horizontal straight lines of 800 points. So that we do an idea to ourselves, a TV set (of any size) has an equivalent resolution of 800x625 points.

As for the number of colors, it turns out to be almost clear: those that the card can present simultaneously for screen. This way, although the cards EGA only represent simultaneously 16 colors, they choose them of a palette (yes, like those of painter) of 64 colors.

The combination of these two parameters is named a video way; they are closely related: to major resolution, minor number of representable colors, and on the contrary. In modern cards (SVGA and Superiors), what ties them is the quantity of memory of video (the one that is present in the card, not the general memory or RAM). Some possible combinations are:

Video memory

Maximum resolution (in 2D)

Maximum number of colors

512 Kb

1024x768 to 16 colors

256 to 640x480 points

1 MB

1280x1024 to 16 colors

16,7 millions to 640x480

2 MB

1600x1200 to 256 colors

16,7 millions to 800x600

4 MB

1600x1200 to 65.536 colors

16,7 millions to 1024x768

The most common ways have been placed, since not all the cards admit all the ways, apart from the fact that many do not allow to extend the video memory. For the onlookers, the calculation of the necessary memory is: (Animal. Vert). x (Animal. Horiz). x (Bits of color)/8.

It is necessary to emphasize that the way of elected video must be supported by the monitor, since if not this one might to get damaged seriously (very seriously). This depends on the characteristics of the same one, in particular on the Horizontal Frequency, as he explains himself in the paragraph dedicated to the monitor.

On the other hand, the resolution ways for graphs in 3D (I based games) usu