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.
The graphics card creates a wire frame image, then fills it
in and adds textures and shading.
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Graphics Card Basics
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.
The four main components of a graphics card are
connections for the motherboard and monitor, a processor, and memory.
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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.
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.
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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
Processor and Memory
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.
A heat
sink or fan keeps a graphics card's processor from overheating.
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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
Integrated Graphics
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.
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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.
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.
Input & Out Put
ADC Connectors
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.
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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.
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.
This Radeon X800XL graphics card has DVI, VGA and ViVo
connections.
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In addition to connections for the motherboard and monitor, some graphics cards
have connections for:
TV display: TV-out or S-video
Analog video cameras: ViVo or video in/video out
Digital cameras: FireWire or USB
Some cards also
incorporate TV tuners.
Next, we'll examine the factors that contribute to a graphics card's speed and
efficiency.
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.
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What Makes 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.
Some cards, like the ATI All-in-Wonder, include
connections for televisions and video as well as a TV tuner.
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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:
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.
Overclocking
Some people choose to improve their graphics card's performance
by manually setting their clock speed to a higher rate, known as
overclocking. 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.
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