how graphics cards work 17 by nafes

7/25/2019 How Graphics Cards Work 17 by nafes

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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 from the C!and turn it

into a picture you can see. !nless a computer has graphics capability built into the

motherboard, that translation takes place on the graphics card.

A graphics card"s #ob is complex, but its principles and components are easy to

understand. $n this article, we will look at the basic parts of a video card and what

they do. %e"ll also examine the factors that work together to make a fast, e&cient

graphics card.

Think of a computer as a company with its own art department. %hen people in the

company want a piece of artwork, they send a re'uest 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 C!, working in con#unction

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.

$t then sends that information to the monitorthrough a cable.

Creating an image out of binary datais a demanding process. To make a (-)image,

the graphics card *rst creates a wire frame out of straight lines. Then,

it rasterizesthe image +*lls in the remaining pixels. $t also adds lighting, texture

and color. or fast-paced games, the computer has to go through this process about

sixty times per second. %ithout a graphics card to perform the necessary

calculations, the workload would be too much for the computer to handle.
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The graphics card accomplishes this task using four main components/

A motherboardconnection for data and power

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

0emoryto hold information about each pixel and to temporarily storecompleted pictures

A monitorconnection so you can see the *nal result

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.

The GPU

ike a motherboard, a graphics card is a printed circuit board that houses

a processorand 2A0. $t also has an input3output system+4$56chip, which stores

the card"s settings and performs diagnostics on the memory, input and output at

startup. A graphics card"s processor, called agraphics processing unit+7!, issimilar to a computer"s C!. A 7!, however, is designed speci*cally for performing

the complex mathematical and geometric calculations that are necessary for

graphics rendering. 6ome of the fastest 7!s have more transistors than the

average C!. A 7! produces a lot of heat, so it is usually located under a heat sink

or a fan.

$n addition to its processing power, a 7! uses special programming to help it

analy8e and use data. T! and n"idiaproduce the vast ma#ority of 7!s on the

market, and both companies have developed their own enhancements for 7!

performance. To improve image 'uality, the processors use/

Fu## scene anti a#iasing+6AA, which smoothes the edges of (-) ob#ects

nisotropic $#tering+A, which makes images look crisper

9ach company has also developed speci*c techni'ues to help the 7! apply colors,

shading, textures and patterns.
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As the 7! creates images, it needs somewhere to hold information and completed

pictures. $t uses the card"s 2A0for this purpose, storing data about each pixel, its

color and its location on the screen. art of the 2A0 can also act as a frame %u&er,

meaning that it holds completed images until it is time to display them. Typically,

video 2A0 operates at very high speeds and is dua# ported, meaning that the

system can read from it and write to it at the same time.

The 2A0 connects directly to the digita#'to'ana#og converter, called the )AC.

This converter, also called the 2A0)AC, translates the image into an analog signal

that the monitor can use. 6ome cards have multiple 2A0)ACs, which can improve

performance and support more than one monitor. :ou can learn more about this

process in ;ow Analog and )igital 2ecording %orks.

The 2A0)AC sends the *nal picture to the monitor through a cable. %e"ll look at

this connection and other interfaces in the next section.

TH( (")*UT!)+ )F G,PH!C- C,-

7raphics cards have come a long way since $40 introduced the *rst one in 1ow, the minimum standard for

new video cards is "ideo Graphics rra0+?7A, which allows @ colors. %ith

high-performance standards like 1uantum (xtended Graphics rra0+B7A,

video cards can display millions of colors at resolutions of up to DED x 1@( pixels.

This ,adeon 23442* graphics card has "!5 "G and "i"o connections.

PC! Connection

7raphics cards connect to the computer through the motherboard.

The motherboardsupplies power to the card and lets it communicate with the C!.

>ewer graphics cards often re'uire 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/
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eripheral component interconnect+C$

Advanced graphics port+A7

C$ 9xpress+C$e

C$ 9xpress is the newest of the three and provides the fastest transfer ratesbetween the graphics card and the motherboard. C$e also supports the use of two

graphics cards in the same computer.

0ost graphics cards have two monitor connections. 5ften, one is a )?$ connector,

which supports C)screens, and the other is a ?7A connector, which

supports C2Tscreens. 6ome graphics cards have two )?$ connectors instead. 4ut

that doesn"t rule out using a C2T screenF C2T screens can connect to )?$ ports

through an adapter. At one time, Apple made monitors that used the proprietary

Apple )isplay Connector +A)C. Although these monitors are still in use, new Apple

monitors use a )?$ connection.

0ost people use only one of their two monitor connections. eople who need to use

two monitors can purchase a graphics card with dua# head capa%i#it0, which splits

the display between the two screens. A computer with two dual head, C$e-enabled

video cards could theoretically support four monitors.

$n addition to connections for the motherboard and monitor, some graphics cards

have connections for/

T? display/ T?-out or 6-video

Analog video cameras/ ?i?o or video in3video out

)igital cameras/ ire%ireor !64

6ome cards also incorporate T? tuners. >ext, we"ll look at how to choose a good

graphics card.

!,(CT2 + )P(+ G*

)irect and 5pen 7 are app#ication programming interfaces, or A$s. An A$

helps hardware and software communicate more e&ciently by providing

instructions for complex tasks, like (-) rendering. )evelopers optimi8e graphics-

intensive games for speci*c A$s. This is why the newest games often re'uireupdated versions of )irect or 5pen 7 to work correctly.

A$s are diGerent from drivers, which are programs that allow hardware to

communicate with a computer"s operating system. 4ut as with updated A$s,

updated device drivers can help programs run correctly.

Choosing a Good Graphics Card
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A top-of-the-line graphics card is easy to spot. $t has lots of memoryand a

fast processor. 5ften, it"s also more visually appealing than anything else that"s

intended to go inside a computer"s case. ots of high-performance video cards are

illustrated or have decorative fans or heat sinks.

4ut a high-end card provides more power than most people really need. eople whouse their computers primarily for e-mail, word processing or %eb sur*ng can *nd all

the necessary graphics support on a motherboardwith integrated graphics. A mid-

range card is su&cient for most casual gamers. eople who need the power of a

high-end card include gaming enthusiasts and people who do lots of (-) graphic

work.

A good overall measurement of a card"s performance is its frame rate, measured

in frames per second +6. The frame rate describes how many complete images

the card can display per second. The human eye can process about @ frames every

second, but fast-action games re'uire a frame rate of at least D 6 to provide

smooth animation and scrolling. Components of the frame rate are/

Triang#es or vertices per second/ (-)images are made of triangles, or

polygons. This measurement describes how 'uickly the 7! can calculate the

whole polygon or the vertices that de*ne it. $n general, it describes how

'uickly the card builds a wire frame image.

Pixe# $## rate/ This measurement describes how many pixels the 7! can

process in a second, which translates to how 'uickly it can rasteri8e the

image.

The graphics card"s hardware directly aGects its speed. These are the hardwarespeci*cations that most aGect the card"s speed and the units in which they are

measured/

7! clock speed +0;8

6i8e of the memory bus +bits

Amount of available memory +04

0emory clock rate +0;8

0emory bandwidth +743s

2A0)AC speed +0;8

The computer"s C!and motherboardalso play a part, since a very fast graphics

card can"t compensate for a motherboard"s inability to deliver data 'uickly.

6imilarly, the card"s connection to the motherboard and the speed at which it can

get instructions from the C! aGect its performance.
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or more information on graphics cards and related topics, check out the links on

the following page.

!+T(G,T( G,PH!C- + )"(,*)C6!+G

0any motherboardshave integrated graphics capabilities and function without a

separate graphics card. These motherboards handle -) images easily, so they are

ideal for productivity and $nternet applications. lugging a separate graphics card

into one of these motherboards overrides the onboard graphics functions.

6ome people choose to improve their graphics card"s performance by manually

setting their clock speed to a higher rate, known as over c#ockings. eople usually

over clock their memory, since over clocking the 7! can lead to overheating. %hile

over clocking can lead to better performance, it also voids the manufacturer"s

warranty.

How GP Works

:ou point, you clickF you drag and you drop. iles open and close in separate

windows. 0ovies play, pop-ups pop, and video games *ll the screen, immersing you

in a world of (-) graphics. This is the stuG we"re used to seeing on our computers.

$t all started in 1


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way to communicate with the graphics card, enhancing both the look and speed of

your computer"s graphics.

Get )& the PC! 7us

$n 1


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Pipe#ining- This method of data organi8ation allows the graphics card to

receive and respond to multiple packets of data in a single re'uest. ;ere"s a

simpli*ed example of this/ %ith A7, the graphics card can receive a re'uest

for all of the information needed to render a particular image and send it out

all at once. %ith C$, the graphics card would receive information on the

height of the image and wait... then the length of the image, and wait... thenthe width of the image, and wait... combine the data, and then send it out.

-ide%and addressing- ike a letter, all re'uests and information sent from

one part of your computer to the next must have an address containing IToI

and Irom.I The problem with C$ is that this IToI and IromI information is

sent with the working data all together in one packet. This is the e'uivalent of

including an address card inside the envelope when you send a letter to a

friend/ >ow the post o&ce has to open the envelope to see the address in

order to know where to send it. This takes up the post o&ce"s time. $n

addition, the address card itself takes up room in the envelope, reducing the

total amount of stuG you can send to your friend. %ith sideband addressing,

the A7 issues eight additional lines on the data packet #ust for addressing.

This puts the address on the outside of the envelope, so to speak, freeing up

the total bandwidth of the data path used to transfer information back and

forth. $n addition, it unclogs system resources that were previously used to

open the packet to read the addresses.

With PCI, texture maps are loaded from the hard drive to system memory, processed by the CPU and then loadedinto the frame buffer of the graphics card.

Photo courtesy Intel Corporation


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ow that the window si8e has been calculated, a perspective transform is used

to move a step closer to pro#ecting the world onto a monitor screen. $n this next

step, we add some more variables.


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6o, a point +, :, Q, 1.D in the three-dimensional imaginary world would have

transformed position of +", :", Q", %", which we get by the following e'uations/

At this point, another transform must be applied before the image can be

pro#ected onto the monitor"s screen, but you begin to see the level of

computation involved -- and this is all for a single vector +line in the imageN

$magine the calculations in a complex scene with many ob#ects and characters,

and imagine doing all this D times a second. Aren"t you glad someone invented

computersL

$n the example below, you see an animated se'uence showing a walk through

the new ;ow 6tuG %orks o&ce. irst, notice that this se'uence is much simpler

than most scenes in a (-) game. There are no opponents #umping out from

behind desks, no missiles or spears sailing through the air, no tooth-gnashing

demons materiali8ing in cubicles. rom the Iwhat"s-going-to-be-in-the-sceneI

point of view, this is simple animation. 9ven this simple se'uence, though, dealswith many of the issues we"ve seen so far. The walls and furniture have texture

that covers wireframe structures. 2ays representing lighting provide the basis for

shadows. Also, as the point of view changes during the walk through the o&ce,

notice how some ob#ects become visible around corners and appear from behind

walls -- you"re seeing the eGects of the 8-buGer calculations. As all of these

elements come into play before the image can actually be rendered onto the

monitor, it"s pretty obvious that even a powerful modern C! can use some help


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doing all the processing re'uired for (-) games and graphics. That"s where

graphics co-processor boards come in.

How Graphics 7oards He#p

6ince the early days of personal computers, most graphics boards have been

translators, taking the fully developed image created by the computer"s C!and

translating it into the electrical impulses re'uired to drive the

computer"s monitor. This approach works, but all of the processing for the image

is done by the C! -- along with all the processing for the sound, player input

+for games and the interrupts for the system. 4ecause of everything the

computer must do to make modern (-) games and multi-media presentations

happen, it"s easy for even the fastest modern processors to become overworked

and unable to serve the various re'uirements of the software in real time. $t"s

here that the graphics co-processor helps/ it splits the work with the C! so that

the total multi-media experience can move at an acceptable speed.

As we"ve seen, the *rst step in building a (-) digital image is creating a

wireframe world of triangles and polygons. The wireframe world is then

transformed from the three-dimensional mathematical world into a set of

patterns that will display on a -) screen. The transformed image is then

covered with surfaces, or rendered, lit from some number of sources, and *nally

translated into the patterns that display on a monitor"s screen. The most

common graphics co-processors in the current generation of graphics display

boards, however, take the task of rendering away from the C! after the

wireframe has been created and transformed into a -) set of polygons. The

graphics co-processor found in boards like the ?oo)oo( and T>T !ltra takes

over from the C! at this stage. This is an important step, but graphicsprocessors on the cutting edge of technology are designed to relieve the C! at

even earlier points in the process.

5ne approach to taking more responsibility from the C! is done by the 7eorce

@ from >vidia. $n addition to the rendering done by earlier-generation boards,

the 7eorce @ adds transforming the wireframe models from (-) mathematics

space to -) display space as well as the work needed to show lighting. 6ince

both transforms and ray-tracing involve serious Joating point mathematics

+mathematics that involve fractions, called IJoating pointI because the decimal

point can move as needed to provide high precision, these tasks take a serious

processing burden from the C!. And because the graphics processor doesn"t

have to cope with many of the tasks expected of the C!, it can be designed to

do those mathematical tasks very 'uickly.

The new ?oodoo @ from (dfx takes over another set of tasks from the C!. (dfx

calls the technology the T-buGer. This technology focuses on improving the

rendering process rather than adding additional tasks to the processor. The T-
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buGer is designed to improve anti-aliasing by rendering up to four copies of the

same image, each slightly oGset from the others, then combining them to

slightly blur the edges of ob#ects and defeat the I#aggiesI that can plague

computer-generated images. The same techni'ue is used to generate motion-

blur, blurred shadows and depth-of-*eld focus blurring. All of these produce

smoother-looking, more realistic images that graphics designers want. Theob#ect of the ?oodoo @ design is to do full-screen anti-aliasing while still

maintaining fast frame rates.

Computer graphics still have a ways to go before we see routine, constant

generation and presentation of truly realistic moving images. 4ut graphics have

advanced tremendously since the days of =D columns and @ lines of

monochrome text. The result is that millions of people en#oy games and

simulations with today"s technology. And new (-) processors will come much

closer to making us feel we"re really exploring other worlds and experiencing

things we"d never dare try in real life. 0a#or advances in C graphics hardware

seem to happen about every six months. 6oftware improves more slowly. $t"s still

clear that, like the $nternet, computer graphics are going to become an

increasingly attractive alternative to T?.

how graphics cards work 17 by nafes

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