How Graphics Cards Work

By: Jeff Tyson, Tracy V. Wilson & Talon Homer  | 

man making video graphics
Graphics cards take the data from your computer's central processing unit (CPU) and turn it into visual information you see on your monitor. SasinT Gallery/Getty Images

The images you see on your computer monitor are made of tiny dots called pixels. At most common resolution settings, a screen displays more than 2 million pixels, and the computer has to decide what to do with each 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. This translator is known as a graphics processor, or GPU.

Most entry-level consumer laptops and desktops now come with a secondary GPU built into their main processor, known as integrated graphics. Pro-level or custom machines, however, will often also have space for a dedicated graphics card. The advantage of a graphics card is that it can typically render more complex visuals much faster than an integrated chip.

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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 60 to 120 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 graphics processor (GPU) to decide what to do with each pixel on the screen
  • Video memory (VRAM) 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.

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The GPU

graphics card
A GPU is an electronic circuit that your computer uses to speed up the process of creating and rendering computer graphics. CHALERMPHON SRISANG/Shutterstock

Like a motherboard, a graphics card is a printed circuit board that houses a processor and VRAM. It also has an input/output system (BIOS) chip that 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.

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A GPU produces a lot of heat, so it is usually located under a heat sink or a fan. Integrated chips differ slightly, in that they don't have their own VRAM, and have to pull from the same RAM stockpile as the CPU. This distinction may cause your system to run short on memory while gaming with an integrated GPU.

In addition to its processing power, a GPU uses special programming to help it analyze and use data. AMD and nVidia produce the vast majority of GPUs on the market, and both companies have developed their own enhancements for GPU performance. Today's video processors can provide:

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 VRAM 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.

Modern video cards plug into a PCIe x16 expansion slot. Small form-factor computers with integrated graphics, such as laptops and mini desktops, may not come with such a slot. Graphics cards can still be connected, however, using a costly workaround device called an external GPU.

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Choosing a Good Graphics Card

A top-of-the-line graphics card is easy to spot. It has lots of memory and a fast processor. Often, it's also more visually appealing than anything else that's intended to go inside a computer's case. Lots of high-performance video cards are illustrated or have decorative fans or heat sinks.

But a high-end card provides more power than most people really need. People who use their computers primarily for email, word processing or social media can find all the necessary graphics support on a CPU with integrated graphics. A mid-range card is sufficient for most casual gamers. People who need the power of a high-end card include gaming enthusiasts and people who do lots of 3-D graphic work.

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A good overall measurement of a card's performance is its frame rate, measured in frames per second (FPS). The frame rate describes how many complete images the card can display per second. The human eye can process about 25 frames every second, but fast-action games require a frame rate of at least 60 FPS to provide smooth animation and scrolling. Components of the frame rate are:

  • Triangles or vertices per second: 3-D images are made of triangles or polygons. This measurement describes how quickly the GPU can calculate the whole polygon or the vertices that define it. In general, it describes how quickly the card builds a wire frame image.
  • Pixel fill rate: This measurement describes how many pixels the GPU can process in a second, which translates to how quickly it can rasterize the image.

The graphics card's hardware directly affects its speed. These are the hardware specifications that most affect the card's speed and the units in which they are measured:

  • GPU clock speed (MHz)
  • Size of the memory bus (bits)
  • Amount of available memory (MB)
  • Memory clock rate (MHz)
  • Memory bandwidth (GB/s)

The computer's CPU and motherboard also play a part, since a very fast graphics card can't compensate for a motherboard's inability to deliver data quickly. Similarly, the card's connection to the motherboard and the speed at which it can get instructions from the CPU affect its performance.

For more information on graphics cards and related topics, check out the links below.

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Originally Published: Mar 16, 2001

Graphics Card FAQ

What does a graphics card do?
A graphics processing unit or GPU is also known as a graphics card. It’s an electronics circuit that accelerates the processing required for creating and rendering images, animations and video.
Is GTX or RTX better?
The GeForce RTX 2060 is considered to be the faster option compared to the GeForce GTX 1070. However, neither of the two have the power to support 4k ultra gameplay.
Which graphics card is best for gaming?
There are many options when it comes to the best graphics card for gaming. It ultimately boils down to personal preference and requirements. The GeForce RTX 3090, 3090 Ti and 3070, along with the Radeon Rx 6800, are all considered to be top tier options for heavy gaming.
Which graphics card is the best from the NVIDIA lineup?
The NVIDIA GeForce RTX 3090 DirectX 12.00 is considered to be the best graphics card from the NVIDIA lineup, which is cloesly followed by the NVIDIA GeForce RTX 3080.
Can you put a graphics card in a laptop?
Most laptops come with built-in graphics cards that are permanently attached to the motherboard. However, for laptops that come with the Thunderbolt 3 port, attaching an external graphics card is possible.

Lots More Information

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More Great Links

  • Hale, Brent. TechGuided. "Dedicated GPU vs. Integrated Graphics." Sept. 29, 2018. (July 27, 2021) https://techguided.com/dedicated-graphics-card-vs-integrated-graphics/
  • Intel.com. "What is the Difference between Integrated Graphics and Discrete Graphics?" (July 27, 2021) https://www.intel.com/content/www/us/en/support/articles/000057824/graphics.html
  • Krüger, Jens. Penn State "GPU Simulation and Rendering of Volumetric Effects" 2005. (July 27, 2021) https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.69.6274&rep=rep1&type=pdf
  • Microsoft.com "How to install the latest version of DirectX" (July 27, 2021) https://support.microsoft.com/en-us/topic/how-to-install-the-latest-version-of-directx-d1f5ffa5-dae2-246c-91b1-ee1e973ed8c2
  • Open GL.(July 27, 2021) http://www.opengl.org
  • Ryan, Thomas and Chacos, Brad. PC World. "How to Install a New Graphics Card." Jan. 4, 2021. (July 27, 2021)https://www.pcworld.com/article/2913370/how-to-install-a-graphics-card.html
  • Smith, Sherri. Laptop Mag. "Best eGPUs" July 19, 2021. (July 27, 2021) https://www.laptopmag.com/articles/best-egpus
  • Techopedia. "What is GPU-accelerated Computing?" (July 27, 2021) https://www.techopedia.com/definition/32876/gpu-accelerated-computing
  • Walton, Jarred. Tom's Hardware. "Graphics Card Buyer's Guide." July 15, 2021. (July 27, 2021) https://www.tomshardware.com/reviews/best-gpus,4380.html
  • Walton, Jarred. Tom's Hardware. "GPU Benchmarks and Hierarchy." July 21, 2021. (July 27, 2021) https://www.tomshardware.com/reviews/gpu-hierarchy,4388.html

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