Computer Questions: How Agp Works

Information about AGP and how it works in simple layman's terms. Explains graphics operations on your PC.

AGP stands for Accelerated Graphics Port and is the architectural standard for the way your PC handles and displays graphics, succeeding PCI (Peripheral Component Interconnect) functions. It was introduced in 1997 by Intel for use in its Pentium II based motherboards but has since become the industry standard for the way graphics is processed on your PC.

AGP delivers graphics performance comparable to what you routinely find on dedicated graphics workstations costing upwards to $20,000, for a fraction of the price. Graphical elements such as texture mapping, z buffering and alpha blending allows for realistic 3D images in games and scientific applications without having to get up off a lot of cash for specialized hardware that couldn't be used for much of anything else.

Now, your eyes probably glazed over at the terms 'texture mapping', 'z buffering' and 'alpha blending'. Well, here is a quick explanation of each and how they work in processing graphics on your video card. Texture mapping is a graphics process that renders a 2 dimensional (2D) image and wraps it around a 3 dimensional object.



Z buffering is an algorithm, or formula, that makes sure perspective works in the virtual world the way it does in the real world. For instance, objects in the foreground blocks those in the back ground. Things such as the display of shadows and line-of-site viewing from the vantage point of the user are also handled as part of the z buffering process.

Alpha blending is the process of determining how each pixel element in an image will behave in terms of opacity versus transparency. Each pixel in 32-bit graphics has four channels: Red, Green, Blue, and an alpha channel, which governs how the previous three in the current pixel look when layered on top of another pixel.

Now how does all this relate to the AGP and your video card? Speed, detail, and frame rate in 3D applications. Frame rate is how many frames can be displayed in a second. This is much faster than the eye can determine image from image, thus giving the illusion of movement and animation when in actuality you are seeing individual snap shots.

PCI based video cards supports a data transfer rate of up to 132 MB/s (megabits per second) in 32 bit graphics, while AGP based cards support up to 533 MB/s. PCI cards must share bandwidth with other peripheral devices in the PC such as the printer port and hard drive controller. It must also preload texture data into video memory. Additionally, PCI cards must perform one instruction at a time. All of this affects graphics performance. Because of the wider bandwidth of data transfer between motherboard processor and your AGP based video card, this blending and texture information is processed on the fly in real time as opposed to being preloaded into your video card's memory and accessed at periodic intervals.

The AGP maintains a higher data transfer rate between video card and motherboard through multiple direct memory queries. It uses your main system memory in a dynamic fashion. That is, memory that is not in use by the graphic card is returned to the operating system on a need to need basis. Because your video card, using the Accelerated Graphics Port, accesses your RAM directly on a wider bandwidth, graphics information is processed faster, resulting in more realistic displays and smoother animations.

Nowadays, AGP slots come standard on motherboards. There is in option in you BIOS setup to allocate a portion of system memory to AGP video functions if the motherboard has an onboard graphics card. The best thing, however, is to purchase an actual AGP graphics card as it will always be better than onboard graphics. Also you need to consider RAM. As AGP functions use actual system RAM, you need to ensure you have enough for that and normal system operation. More memory equals better graphics performance and smoother all around PC operations.

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