How Graphics Cards Work

I found this article about Video cards in How Stuff Works. I think it is a pretty good introduction and straight forward, which should help understand what is the video cards job in a computer. I think it is worth to note that this article is old. Although most cards will stay on this concept there are a few notes that I will add to the bottom

Computer Hardware Image Gallery

Computer Hardware Image Gallery

Graphics cards take data from the CPU and turn it into pictures. See more computer hardware pictures.

Introduction to How Graphics Cards Work

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, itrasterizes 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.

Graphics cards take data from the CPU and turn it into pictures. Find out the parts of a graphics card and read expert reviews of graphics cards.

2008 HowStuffWorks

The GPU

Like a motherboard, a graphics card is a printed circuit board that houses a processor andRAM. 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.

The RAMDAC sends the final picture to the monitor through a cable. We’ll look at this connection and other interfaces in the next section.

THE EVOLUTION OF GRAPHICS CARDS

Graphics cards have come a long way since IBM introduced the first one in 1981. Called a Monochrome Display Adapter (MDA), the card provided text-only displays of green or white text on a black screen. Now, the minimum standard for new video cards is Video Graphics Array (VGA), which allows 256 colors. With high-performance standards like Quantum Extended Graphics Array (QXGA), video cards can display millions of colors at resolutions of up to 2040 x 1536 pixels.­

This Radeon X800XL graphics card has DVI, VGA and ViVo connections.

PCI Connection

Graphics cards connect to the computer through the motherboard. The motherboard supplies power to the card and lets it communicate with the CPU. Newer graphics cards often require more power than the motherboard can provide, so they also have a direct connection to the computer’s power supply.

Connections to the motherboard are usually through one of three interfaces:

PCI Express is the newest of the three and provides the fastest transfer rates between the graphics card and the motherboard. PCIe also supports the use of two graphics cards in the same computer.

Most graphics cards have two monitor connections. Often, one is a DVI connector, which supports LCD screens, and the other is a VGA connector, which supports CRT screens. Some graphics cards have two DVI connectors instead. But that doesn’t rule out using a CRT screen; CRT screens can connect to DVI ports through an adapter. At one time, Apple made monitors that used the proprietary Apple Display Connector (ADC). Although these monitors are still in use, new Apple monitors use a DVI connection.

Most people use only one of their two monitor connections. People who need to use two monitors can purchase a graphics card with dual head capability, which splits the display between the two screens. A computer with two dual head, PCIe-enabled video cards could theoretically support four monitors.

In addition to connections for the motherboard and monitor, some graphics cards have connections for:

Some cards also incorporate TV tuners. Next, we’ll look at how to choose a good graphics card.

DIRECTX AND OPEN GL

DirectX and Open GL are application programming interfaces, or APIs. An API helps hardware and software communicate more efficiently by providing instructions for complex tasks, like 3-D rendering. Developers optimize graphics-intensive games for specific APIs. This is why the newest games often require updated versions of DirectX or Open GL to work correctly.

APIs are different from drivers, which are programs that allow hardware to communicate with a computer’s operating system. But as with updated APIs, updated device drivers can help programs run correctly.­

Some cards, like the ATI All-in-Wonder, include connections for televisions and video as well as a TV tuner.

Photo courtesy of HowStuffWorks Shopper

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 e-mail, word processing or Web surfing can find all the necessary graphics support on a motherboard 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.

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)
  • RAMDAC speed (MHz)

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 on the following page.

INTEGRATED GRAPHICS AND OVERLOCKING

Many motherboards have integrated graphics capabilities and function without a separate graphics card. These motherboards handle 2-D images easily, so they are ideal for productivity and Internet applications. Plugging a separate graphics card into one of these motherboards overrides the onboard graphics functions.

Some people choose to improve their graphics card’s performance by manually setting their clock speed to a higher rate, known as overclockings. People usually overclock their memory, since overclocking the GPU can lead to overheating. While overclocking can lead to better performance, it also voids the manufacturer’s warranty.

Lots More Information

Related HowStuffWorks Articles
More Great Links
Sources

Added notes: although the article has a section on how to chose a video card, using only numbers won’t help a lot. To chose the correct video card, you need to have in consideration, power requirements, heat dissipation and application. Although this sounds more complicated it is easy to relate to.

  • Power Requirements. Your Power supply not only needs to provide enough steady power (Watts), but you also need to consider if the extra power is worth it. Sure, you can spend $500 on a video card and not have to worry about being fast enough, however your electric bill will be higher, and your PSU (Power Supply Unit) will need to provide probably +650 Watts for a card of that caliber
  • Heat Dissipation: more power usually means more heat, but not always. As technology advances, companies are getting better at optimizing the components so they can computer the same amount with less power, and less heat. For example, NVIDIA GF100 GPU (Ferni) (GeForce GTX 465/470/480) were powerful GPUs, but the GF110 (GeForce GTX 560/570/580) produced considerable less heat (1)
  • Application: this is a bit more difficult to quantify. If you are a gamer, what kind of games will you play? How long are you planning to keep your current setup and budget. If you do multimedia, to what extend? Do you edit video and pictures? Do you only browse the web? Will you use Windows 7?
    • All this questions have different answers.  A very common problem I saw with Vista and Windows 7 was inappropriate graphics cards. Not playing video games, does not mean a cheap graphic card. Windows will still use the graphics card if it can to draw your desktop, so a slow graphics card means the CPU might end up doing the work instead, and performance will suffer a hit.
    • Multimedia is also an important factor, video and image editing software can use video cards to process. This is kind of new on mainstream. Since a GPU is faster than a CPU Photoshop CS5.5 can work faster on images when using NVidia cards with CUDA support or AMD with OpenGL 2.0.
    • Some video encoding software also uses specific video cards to offload work to the GPU. I have personally tested a couple, and while the conversion process was not faster, because the GPU was doing the work, I was able to do other stuff like document editing and web browsing without feeling the computer slow.

To chose a video card I suggest using Toms Hardware Best Graphics card for the money. It is still not perfect science, but it will steer you a lot better in the right direction.

Integrated video: Although sufficient for most cases, it might not always be so. For example, and older computer with Windows 7, might not display the desktop correctly. The fix would be to change the theme to a basic setup (which removes a lot of effects in favor of performance) or getting a inexpensive graphics card. The cheapest card in Toms’s hardware list  (~$75) will be more than enough for this.

While talking about integrated video, I can also point out that I feel AMD’s FUSION (APU) solutions to be more responsive in video than Intel (Core ix). I consider Intel integrated graphics (HD graphics 3000/2000)  to be adequate only for light graphics, and windows experience score is proof of that. However it will be enough for Blu-ray in most cases**

Integrated and Blu-ray: decoding (playing) Blu-ray can be quite heavy. If the video card is not doing the decoding then the CPU will do the decoding. There is also a consideration for the sound which is protected over HDMI, falling back to a lower encoding if not on protected channel. This is beyond the scope, but should be considered if the main use will be blu-ray playing.

Motherboard connection: Many mid to high end cards will take 2 slots on the motherboard. This is a special consideration on multi graphic cards setup (SLI/CrossFire) since 2 cards would take 4 expansion slots and 3 would take 6, which will also make cooling and power more of an issue.

When the article was explaining about the connectors (VGA, DVI) it is not accurate. There are LCD monitors with only VGA, as well as CRT monitors with BNC connectors. CRT have a higher refresh rate producing crispier image, although LCD are getting to those levels now and even surpassing on higher end models.

There are also HDMI and display port. HDMI is similar to DVI, but can carry audio signal (if graphics cards allows it).

Display port is a bit more complicated, but more interesting. Check this link for information

http://www.techradar.com/news/computing/hdmi-vs-displayport-which-is-best–922876?artc_pg=2

Update for January 22, 2016: it has been 4 years since the article, and the information still valid. However a few more updated notes

CRT monitors are difficult to find. They still produce the sharpest image when using a good quality monitor, but OLED is aiming to fix that.

New issues with choosing video cards now are the monitors in use, and the intended quality. Most likely people looking for a video card are planning to play video games in the computer. With 4K, 2K, WQHD resolutions and all high resolutions a better video card is needed to play the games in those resolutions.

For example, the LG 25UM57-P is a 25″ monitor with a resolution of 2560×1080 (2K). The famous 1080p resolution is actually 1920×1080, this means that there is 640×1080 more pixels to draw. And it does help, because the HUD components are not in the middle anymore. But it will require a bit more power.

Another problem with that, is that not all games with support those resolutions, but that is outside the scope of this article. For that use something like Flawless widescreen

4K monitors, bring the point I just made to  whole higher level. 4K is 3840 × 2160, but can be 4096 x 2160 and even 5120 x 2160 in Ultra Wide format. This is twice the resolution of 1080, which means twice the data has to be draw and sent to the monitor.

So, you are probably thinking, OK, I need a more powerful video card for the higher resolutions, but that is not all.

Because it is twice the data, the connection is important as well. I use 2K monitors, and they will only offer that resolution if connected by dual DVI-D or Display Port, and not on HDMI or VGA. So now the connectors are important as well.

This is not the same for all and depends a lot on the HDMI used. For example HDMI 1.4 supports 4K, but at 25Hz, HDMI 2.0 supports 4K up to 60 fps.

For HDMI version char visit the following Wikipedia article

https://en.wikipedia.org/wiki/HDMI#Version_comparison

3D will be something else to consider, and will require a special monitor as well, and gets the topic more complex. I won’t even touch virtual reality because it is too new at the moment.

I personally would say, at those levels don’t bother with HDMI, and instead of Display Port. The reason for that is that most 2K and higher monitors will have Display Port (or mini display port), so as long as your video card has the port it is a safer connection to get the best quality

Update about the need of powerful cards:

Toms Hardware has a good articles about best CPUs for gaming. But wait, this is a video card article, why are we talking about CPU? Easy, the CPU charts pretty much say that a Core i5 is great for gaming, and that a Core i7 wont give you much. So, expend that budget on video cards. Great advice, except for one thing

There are circumstances where you won’t need more video power. This is changing a lot at the moment, but not fast enough either.

PC gaming has been lagging lately. It is an undeniable truth that most gaming happens in consoles, and consoles is where the money is for developers. After all, they charge more for the console version than they do for the PC, and PC games prices tend to discount much faster and farther than consoles.

So, generally what has happened for the last 7 years, is that a game was developed for Xbox360 and PS3, and then ported to PC. The ported PC version generally came from Xbox360, but the Xbox360 has a different CPU architecture so the ports are not perfect.

This results in games capping at 60fps, 1080 with max resolution, or high details that are very minimum compared to medium details. Some ports had just awful quality and looked like PS2 versions (and some ports are from PS2 directly). This games don’t generally tax the video card, or some taxed the video card only when 1 setting was enabled (because it was improperly applied, or ported).

So, now PS4 and Xbox One are out. 4th Generation consoles that can run games at 1080/60fps. Does this mean we need more powerful video cards? Not really. The video cards are already more powerful that what is inside the console, but games are still not optimize to the new consoles. The consoles are about 2 years old, and still not a lot of games run at 1080/60fps, but instead they run at 1080/30fps. PC games have been running at 1080 and way above 60 fps for a long time.

What is does mean is that we will see more demanding games, but at the moment my Radeon HD 7870 which is a few years old, still can play most games that I own on the highest settings

**Update for Integrated video. Integrated video has come a long way since 4 years ago. I have tested and used a lot of integrated video, and I have been pleasantly surprised.

In no way Integrated video can compare to a dedicated video card, but the 6th generation of Intel HD graphics (Intel Core i3/5/7 6xxx)can support up to 3 displays, and most configurations will have at least a mini Display Port. This is important because before for multi monitor setups for office I would have used a dedicated video card. Now a days I use the integrated video, and I even have a Gigabyte Brix Pro that has the Intel Iris  video and can play Tomb Raider at a comfortable medium detail level.

The Intel HD graphics also has quick sync for video decoding which actually does help.

In summary, video cards changed a lot. Reading the article will help understand how they work, but a lot has changed, and will continue to change, so it is a moving target.

Check Toms Hardware web site for the graphics card chart and Best graphics card for the money to get more specific and updated recommendations. They update the recommendations monthly.

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