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Video Cards

Oct 08, 1999 2929 Words
Video Cards


People are living in a three-dimensional space. They know what is up, down, left, right, close and far. They know when something is getting closer or moving away. However, the traditional personal computers can only make use of two dimensional space due to relatively low technology level of the video card in the past. As the new technology has been introduced to the video card industry in recent years, the video card can now render 3D graphics. Most of the PC computer games nowadays are in three dimensions. In addition, some web sites also apply the use of three dimensional space. This means that they are no longer a flat homepage, but instead a virtual world. With that added dimension, they all look more realistic and attractive. Nevertheless, 3D do not exist in most of the business programs today, but it can be forecasted that it is not far away.

Many new kinds of video cards have been introduced to the market recently. In the past, the video card could only deliver two dimensional graphics which were only in low resolution. However, there has now emerged as a result of high resolution three dimensional graphics technology. This paper will discuss why the video card nowadays can process high resolution three dimensional graphics, but why the video card in the past could only process low resolution two dimensional graphics. The explanation will be based on some recently developed video cards such like Matrox Millennium. This paper will also discuss how the 3D graphic displays on a 2D monitor. Lastly, the video card, Matrox Millennium, will also be discussed.

Basic principles

In order to understand the recent development of the video card, let's take a look on how a video card works.

The video card is a circuit, which is responsible for processing the special video data from the central processing unit (CPU) into a format that the visual display unit (VDU) or monitor can understand, to form a picture on the screen. The Video Chipset, the Video Memory ( Video RAM ) and the Digital Analog Converter ( RAM DAC ) are the major parts of a video card.

After the special video data leaves the CPU, it has to pass through four major steps inside the video card before it reaches the VDU finally. First, the special video data will transfer from the CPU to the Video Chipset, which is the part responsible for processing the special video data, through the bus. Secondly, the data will transfer from the Video Chipset to the Video Memory which stores the image displayed on a bitmap display. Then, the data will transfer to the RAM DAC which is responsible for reading the image and converting the image from digital data to analog data. It should be noted that every data transfer inside the computer system is digital. Lastly, the analog data will transfer from the RAM DAC to the VDU through a cable connected between them outside the computer system.

The performance of a video card is mainly dependent upon its speed, the amount and quality of the Video Memory, the Video Chipset and the RAM DAC.

The faster the speed, the higher the picture quality and resolution the video card can deliver. This is due to the fact that the picture on the VDU has to change continuously, and this change must be made as fast as possible in order to display a high quality and realistic image. In the process of transferring data from the CPU to the Video Chipset, the speed is mainly dependent upon the type and speed of the bus, the mainboard and its chipset.

The amount of the Video Memory is also responsible for the color and screen resolution. The higher the amount of the Video Memory, the higher the color depth the video card can render. On the other hand, the type of the Video RAM is an another factor that affects the speed of the video card.

The Video Chipset is the brain of a video card. It similar to the CPU in the motherboard. However, unlike the CPU which can be fitted with different motherboards, certain Video Chipsets can only be fitted with certain video cards. The Video Chipset is responsible for processing the special video data received from the CPU. Thus, it determines all the performance aspects of the video card.

The RAM DAC is the part responsible for the refresh rates of the monitor. The quality of the RAM DAC and its maximum pixel frequency, which is measured in MHz, are the factors affecting the refresh rates. In fact, a 220 MHz RAM DAC is not necessarily but most likely better than a 135 MHz one.

Recent developments

Traditionally, the personal computer can only deliver two dimensional pictures. However, as people want to increase their living standards, they want the picture on their personal computer be more realistic and attractive. Thus, the display of three dimensional pictures in the personal computer is being developed. The rendering of the 3D image requires the computer to update the screen of the VDU at least 15 times per second as the one navigate through it, and each of the objects have to go through the transformation in depth space which is known as the z-axis, and is on the coordinate of the x-y plane. Nevertheless, the video card in the past was not "powerful" enough to render the three dimensional graphics. The introduction of some new kind of video cards in recent years has solved this problem, and are able to render 3D graphics now.

In the past, the video card could only deliver two dimensional graphics because the technology at that time limited what they can do. One of the problems is that the speed of the transfer of data from the CPU to the Video Chipset was relatively low, but it is actually not the problem associated with the video card. It is associated with the type of the CPU, the bus and the motherboard in the computer system. On the other hand, the biggest problem is actually the quality of Video RAM. The Video RAM is the part in a video card which is situated between two very busy devices, the Video Chipset and the RAM DAC; and the Video RAM has to serve both of them all the time. Whenever the screen has to change, the Video Chipset has to change the content in the Video Memory. On the other hand, the RAM DAC has to read the data from the Video Memory continuously. This means that when the Video Memory is reading the data from the Video Chipset, the RAM DAC has to wait aside. Whenever the video card has to render three dimensional graphics, the screen has to change at least 15 times per second which means that more data has to be transferred from the Video Chipset to the Video Memory, and the data has to be read faster by the RAM DAC. However, the video card, or referred to as the Video Memory, at that time did not have such technology to achieve this kind of process. Thus, the video card in the past was not able to deliver three dimensional graphics.

In recent years, the video card manufacturer has developed some high technology to solve the problem of the poor Video Memory. They have found three different ways to deal with this problem which involves using a higher quality of Video Memory, increasing the video memory bus size, and increasing the clock speed of the video card.

1 ) Dual ported Video RAM

The major step is to make the Video RAM dual ported. This means that when data is transferred from the Video Chipset to the Video Memory via one port, the RAM DAC can read the data from the Video Memory through an independent second port. Thus, these two processes can occur at the same time. Both the Video Chipset and the RAM DAC need not wait for each other anymore. This kind of RAM is called VRAM. Of course, the technology applied is not just double the port in the RAM; it is actually very complicated. Thus, VRAM is more expensive than the normal one.

The invention of the VRAM can offer a higher refresh rate and higher color depth of the graphic on the monitor. The high refresh rate means that the RAM DAC will send a complete picture to the monitor more frequently. Therefore, the RAM DAC has to read the data from the Video Memory more often. However, when the video card in the past, which without the VRAM, wants to achieve this high refresh rate, it has to lower the video performance as the Video Memory cannot afford this kind of heavy work load. As to maintain the high refresh rate and high video performance at the same time, the VRAM has to be used since this kind of RAM can serve the Video Chipset and the RAM DAC at the same time. Thus, the video card need not reduce the video performance when a higher refresh rate occurs. On the other hand, to archive the high color depth, the Video Memory has to read more data from the Video Chipset per time, and thus more data will be sent to the RAM DAC . This process will surely take a longer time. At an8 bit color resolution ( 256 color ), a 1024 ´ 768 screen needs 786432 bytes of data to be read by RAM DAC from the Video Memory. For the same screen, a 24 bit color resolution ( 16777216 color) needs 2359296 bytes of data to be read by the RAM DAC. For similar reasons, if the video card in the past wants to archive this kind of high color depth, it has to lower the refresh rate. This problem can also be solved by the use of the VRAM. In short, the new video card with VRAM can provide a high refresh rate and high color depth at the same time. Thus, the render of three dimensional graphics is possible now.

The WRAM is used in the Martox card instead of the VRAM. The WRAM is developed by the Martox company. It is such like the VRAM which is dual ported. However, the WRAM is designed smarter than the VRAM, so it is faster. Ironically, the WRAM is even cheaper than the VRAM.

Lastly, there are many different types of the Video RAM such as DRAM (Dynamic RAM), EDO DRAM (Extended Data Out DRAM), SDRAM (Synchronous DRAM), SGRAM (Synchronous Graphics RAM), MDRAM (Multibank DRAM), and RDRAM (RAMBUS DRAM). Unlike the VRAM and WRAM, they are all single ported and so are slower. The DRAM is the slowest one amongst all of them.

2 ) Increase video memory bus size

Three years ago, the release of the 32 bit video card amazed people all over the world. However, the 64 bit video card is being introduced nowadays, which has a 64 bit video memory bus inside it. In addition, the 128 bit video card is also available. The video memory bus is a path which links the Video Chipset, the Video RAM and the RAM DAC together. With the 64 bit video memory bus, 8 bytes of data can be transferred in one clock cycle while 4 bytes data with 32 bit video memory bus. Thus, the amount of data transfer is doubled with the use of the 64 bit video card. It is important to notice that a 1 MB Video RAM usually has only a 32 bit data bus. Thus, a 64 bit video card should always work with at least 2MB Video RAM; otherwise, this 64 bit video card will not be able to use its 64 bit data path. All in all, with the use of a 64 bit video card, more data can be transferred at one time. Thus, it actually can shorten the time to transfer data from the Video Chipset to the Video RAM or from the Video RAM to the RAM DAC. This means that a higher color resolution graphic can be rendered.

3 ) Increase the clock speed

The third one is the most obvious one which just increases the clock speed of the Video Chipset and the Video RAM. Of course, the technology to increase the clock speed is very complicated. The fastest Video Chipset so far is the ET 6000 chipset which can run at 100 MHz, while the fastest video memory is SDRAM which can run at clock speed up to 125 MHz. The SDRAM is a special graphic version of SDRAM ( synchronous DRAM ). It is not just the job of the video card to archive high resolution three dimensional graphics. The video card has to work with a good computer system. To recall the speed of the transfer of the data from the CPU to the Video Chipset is mainly dependent upon the bus type, the mainboard and its chipset. Thus, a good computer system to perform good graphics should have a PCI bus which runs at 33MHz with Pentium processor, a Pentium processor with MMX technology, and a good mainboard such as Intel 430 HX chipset which will affect the PCI performance.

3D graphics on 2D monitor

Although the video card can render 3D graphics now, the monitor that the graphic displays on is still flat two dimensions. Thus, the three dimensional graphic has to be mapped to the 2D screen. This is done using perspective algorithms. This means that if an object is farther away, it will appear smaller; if it is closer, it will appear larger. To display 3D animations, an object is first presented as a set of vertices in a three dimensional coordinates which is x, y, z axes. The vertices of the object is then stored in the Video RAM. Afterwards, the object has to be rendered. Rendering is a process, which referred to calculate the different color and position information, which will make the user believe that there is a 3D graphic on a flat 2D screen. To make the calculation more efficiently, the vertices of the object are segmented into triangles. Rendering also fills in all of the points on the surface of the object which were only saved as a set of vertices previously. In this way, an object with 3D effect is able to display on a flat 2D monitor.

A new video card - Matrox Millennium

Lastly, let's discuss some new features of a new video card – Matrox Millennium. Matrox Millennium is a 64-bit video card. It can be work with 2MB or 4MB or even 8MB video RAM. The video RAM are the Matrox company authorized WRAM. It also has a powerful 220 MHz RAMDAC. Actually, it is the fastest video card available in the market now. However, according to its extreme high speed, the graphics quality is relatively lower when compared to other video cards.

The following is a summary of the new 3D features of the Matrox Millennium:

Texture mapping :

This applies bitmapped texture images which are stored in memory to objects in the screen so as to add realism.

Bilinear and trilinear filtering :

They smooth textures in a scene to lessen the blocky effect. With MIP ( multim in parvum ) mapping, an application provides different resolutions of an object as they move closer or further in the screen.

Perspective correction :

This rotates the texture bitmaps to give a better sense of convergence. Thus, when the video card renders a continuous moving object such as a meadow, it is able to maintain a realistic look as it recedes from the viewer.

Anti - aliasing :

This diminishes the "stair step" effect since the computer generated image has a finite discrete resolution.

Alpha blending :

This allows one object to show through another to create a transparent look.

Atmospheric effects :

This usually make use of the alpha blending. The effects are like fog and lighting cues.

Flat shading :

This is a technique where an whole triangle is a single color. Thus, this can create a blocky effect.

Gouraud shading :

This is a more advance method than the flat shading. It improves the overall appearance of the graphics and allows curves to be more round.

Z-buffering :

This techniques is one of the most important features to render 3D graphics. This controls how objects overlay one another in the third dimension. It is particularly important when filled polygons are included in the drawing. With Z buffering off, objects are drawn in the order in which they are transmitted to the display. With Z buffering on, objects are drawn from the back to the front.

Matrox Millennium can also playback a movie with the use of Moving Picture Experts Group (MPEG). With this technology, the video card can compress the movie data into a special format. With the Chroma-key feature, the video card also supports for "blue-screen" video effects, so that two unrelated displays can easily be pasted together. Moreover, if the video card has the Image scaling feature, it can map a video onto any window or screen size desired.



· PC Magazine - December 3, 1996, Vol. 15, NO. 21


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