How Graphics Cards Work by Jeff Tyson and Tracy V. Wilson

How Graphics Cards Work

by Jeff Tyson and Tracy V. Wilson

The images you see on your monitor are made of tiny dots called pixels. At most common resolution settings, a screen displays over a million pixels, and the computer has to decide what to do with every one in order to create an image. To do this, it needs a translator -- something to take binary data from the CPU and turn it into a picture you can see. Unless a computer has graphics capability built into the motherboard, that translation takes place on the graphics card.

A graphics card's job is complex, but its principles and components are easy to understand. In this article, we will look at the basic parts of a video card and what they do. We'll also examine the factors that work together to make a fast, efficient graphics card.

Think of a computer as a company with its own art department. When people in the company want a piece of artwork, they send a request to the art department. The art department decides how to create the image and then puts it on paper. The end result is that someone's idea becomes an actual, viewable picture.

A graphics card works along the same principles. The CPU, working in conjunction with software applications, sends information about the image to the graphics card. The graphics card decides how to use the pixels on the screen to create the image. It then sends that information to the monitor through a cable.

Creating an image out of binary data is a demanding process. To make a 3-D image, the graphics card first creates a wire frame out of straight lines. Then, it rasterizes the image (fills in the remaining pixels). It also adds lighting, texture and color. For fast-paced games, the computer has to go through this process about sixty times per second. Without a graphics card to perform the necessary calculations, the workload would be too much for the computer to handle.

The graphics card accomplishes this task using four main components:

A motherboard connection for data and power

A processor to decide what to do with each pixel on the screen

Memory to hold information about each pixel and to temporarily store completed pictures

A monitor connection so you can see the final result

Next, we'll look at the processor and memory in more detail.

The GPU

Like a motherboard, a graphics card is a printed circuit board that houses a processor and RAM. It also has an input/output system (BIOS) chip, which stores the card's settings and performs diagnostics on the memory, input and output at startup. A graphics card's processor, called a graphics processing unit (GPU), is similar to a computer's CPU. A GPU, however, is designed specifically for performing the complex mathematical and geometric calculations that are necessary for graphics rendering. Some of the fastest GPUs have more transistors than the average CPU. A GPU produces a lot of heat, so it is usually located under a heat sink or a fan.

In addition to its processing power, a GPU uses special programming to help it analyze and use data. ATI and nVidia produce the vast majority of GPUs on the market, and both companies have developed their own enhancements for GPU performance. To improve image quality, the processors use:

Full scene anti aliasing (FSAA), which smoothes the edges of 3-D objects

Anisotropic filtering (AF), which makes images look crisper

Each company has also developed specific techniques to help the GPU apply colors, shading, textures and patterns.

As the GPU creates images, it needs somewhere to hold information and completed pictures. It uses the card's RAM for this purpose, storing data about each pixel, its color and its location on the screen. Part of the RAM can also act as a frame buffer, meaning that it holds completed images until it is time to display them. Typically, video RAM operates at very high speeds and is dual ported, meaning that the system can read from it and write to it at the same time.

The RAM connects directly to the digital-to-analog converter, called the DAC. This converter, also called the RAMDAC, translates the image into an analog signal that the monitor can use. Some cards have multiple RAMDACs, which can improve performance and support more than one monitor. You can learn more about this process in How Analog and Digital Recording Works.