|Video card information
There are quite a few things which you have to consider before selecting a video card. The following list has links to each of them. If you've been around computers for a while then you already know what to do for most of them and you can just skip those. If you haven't done a lot of computer upgrading then it's a good idea to read through all of them. It's easy to overlook something and end up with the wrong video card.
To add a video card to your computer, you have to pick an expansion slot. There have been many kinds of expansion slots over the years so most motherboards contain more than one kind of slot. The usually have a few of the older slots and a few of the newer ones. The slots differ greatly in speed so you need to pick the right kind of slot.
The best expansion slot for a video card is a PCI-Express x16 slot. It is easily the fastest video card slot and it has the best selection of video cards all the way from low-end cards to high-end cards. If you're building or buying a new computer then be sure to get one which has a PCI-Express x16 slot. Some computers with integrated graphics do not have one to save costs. You should avoid buying that kind of computer because the lack of a PCI-Express x16 slot cripples your ability to upgrade the video capabilities in the future. The future of expansion slots is definitely PCI-Express so you should avoid all of the other choices if buying a new computer.
The next best choice is an AGP slot. AGP slots were the standard video card slot before PCI-Express come along. AGP slots do not provide the raw hardware speed of PCI-Express x16 slots. But as of the end of 2006, AGP still provides almost as much gaming performance as PCI-Express x16 because games don't yet require the full performance of PCI-Express x16. In the future, however, PCI-Express x16 will have a performance advantage over AGP. The selection of AGP video cards is starting to get quite limited compared to PCI-Express x16. The fastest video cards are not available for AGP at all. And the AGP version of a video card is usually more expensive than the equivalent PCI-Express x16 card. AGP video cards and motherboards come in different speeds which makes compatibility look complicated. The most common AGP video cards are AGP 8X,4X cards. Those video cards are compatible with all AGP 8X or AGP 4X motherboards. You can read the full rules of AGP compatibility on this page. AGP is quickly becoming obsolete so you should avoid buying a new computer with an AGP slot.
The worst choice to hold a video card is a PCI slot. People normally only use PCI slots to hold their main video card if they made the mistake of buying a computer which didn't have an AGP or PCI-Express x16 slot. There are very few choices of video cards available for PCI and they tend to be slow, obsolete, and overpriced. PCI slots are okay for secondary video cards as long as you don't expect much 3D graphics performance. A PCI slot gives acceptable 2D graphics performance in most situations.
If you would like more detailed information about the various kinds of video card expansion slots and their compatibility rules, then check this page.
Your video card is responsible for sending the video signal through a cable to your monitor. There are two ways to do that: the old analog way, and the new digital way.
The old analog way of doing things is the VGA standard which was introduced in 1987. Almost all CRT monitors (the big, heavy ones which use TV-like tubes) use the VGA standard. Even though VGA is an old analog standard, it still works pretty well. Video transmitted in VGA gets to the monitor in pretty good shape. About the only time there is any image degradation is with very high screen resolutions and refresh rates.
VGA compatibility is very simple. Any VGA monitor will work when connected to the VGA output on any video card. About the only limitation is that some older low-end video cards may not support a high enough screen resolution for some high-end monitors. Most DirectX 9 and newer video cards support high enough screen resolutions and screen refresh rates to support any VGA monitor. If your video card doesn't support a high enough resolution then you're stuck running the monitor at a lower resolution or refresh rate. The way to avoid that is to check the card's specifications on the manufacturer's website. That will tell you the maximum screen resolutions and refresh rates it can support.
If you run your VGA monitor at a high resolution, say 1280 x 1024 or above, then you should avoid extreme low-end video cards. The analog VGA output on some of them can smear high resolution images. Some cheap video cards skimp on the video output filter components to save costs. It's not that easy to know which video cards smear the image and which don't because cheap cards are seldom reviewed. So unless you can find a review which states that the exact low-end card has good 2D image quality then you should avoid the cheapest cards. And don't expect a VGA output which uses a ribbon cable (as shown above) to generate great image quality at high resolutions. If you stick with DirectX 9 cards (newer cards tend to be more careful about VGA image quality) and avoid ribbon cable outputs and cheapy US$40 video cards, then your 2D image quality should be fine even at high resolutions.
The old analog VGA way of doing things has been replaced by a new digital standard: DVI. DVI supports the new digital method of transmitting the video image to your monitor. The digital approach avoids the image degradation which can happen to analog VGA video signals. Digital also makes it possible to display perfectly sharp images on LCD monitors (the thin flat panel monitors). Most LCD monitors accept digital video signals. There are some older low-end LCD monitors which only accept the older analog VGA signals.
There are quite a few varieties of DVI so compatibility can get a bit complicated. This page gives a detailed description of the different kinds of DVI implementations. There are two main kinds of DVI connectors found on video cards and monitors: DVI-D, and DVI-I. DVI-D is the kind of DVI which supports digital video signals only. DVI-I supports both digital and analog (VGA) video signals. A DVI-I video card output can be connected to either digital monitors or analog monitors. A DVI-D video card output can be connected only to digital monitors and cannot drive VGA monitors.
The other issue you should consider with DVI is the number of links. As of the end of 2006, most video card digital DVI outputs are single link outputs. That means that they can only drive monitors up to 1600 X 1200 screen resolution (although sometimes they can go a little higher under certain circumstances). In order to support monitors with more resolution, you need to get a video card with a dual link DVI output. At the moment, dual link DVI outputs are fairly uncommon except on high-end video cards. You can read more about single and dual link DVI on this page.
Most video cards come with two separate monitor outputs. You can hook a monitor to each output and run them simultaneously. If you often wish you had more screen space, then running multiple monitors is the way to go. Older video cards often have one VGA output and one DVI output. Newer video cards usually have two DVI outputs. It's okay to run both analog and digital monitors at the same time. There are a few cards out there which support three simultaneous outputs.
If your computer has integrated graphics, then adding an AGP or PCI-Express x16 video card will probably disable the integrated graphics. It varies from case to case so you have to check the computer specifications to find out if you can run your integrated graphics and an AGP or PCI-Express x16 video card simultaneously. Quite often, the manufacturers don't tell you whether or not it's disabled when you add a video card so you may have to phone the manufacturer to find out. Adding a PCI video card does not disable integrated graphics so you can always use them for multi-monitor setups (assuming you can live with PCI's slow performance).
Most video cards also have some kind of TV output. Almost all of these outputs support both composite and S-Video signals. Composite is basically a "standard" television signal. S-Video is a slightly improved video signal. Both of these are too fuzzy to use for anything like word processing or many other computer-oriented chores. You can use them to view DVD movies and play video games on your computer and see the display on your TV. Many video cards also have some kind of HDTV support. Good HDTVs have enough image resolution to be able to function as a computer monitor. In most cases, if a video card has two monitor outputs as well as a TV output, you cannot use the TV as a third monitor. The TV output is connected to one of the two monitor outputs so the TV output cannot function as a separate third output. It just gives you the option to display a copy of one of the two monitor outputs on a TV.
You can get a general idea of the capabilities of a given video card by checking its technology generation. There's more than one way to count video card generations but the most commonly used is the version of DirectX the video card was designed to support. DirectX is the name for Microsoft's standard for controlling video cards. DirectX was originally released in 1995. DirectX 10 is the most recent version and was released with Windows Vista. DirectX 10 is not supported in previous versions of Windows.
You probably know that the main processor chip in your computer is called the CPU. CPUs are the infinitely flexible computing gizmos which make your computer capable of doing many different things. CPUs are programmable. You just load up the right program and you can get a CPU to do just about anything. Video cards have their own main processor chip called a GPU. The biggest makers of the GPUs you find on video cards are NVIDIA and ATI. Intel makes most of the integrated video GPUs you find built into motherboards. A GPU is not as flexible as a CPU although the newer GPUs are definitely more flexible than the older ones. A GPU has two very different jobs: drawing two dimensional graphics (2D) and drawing three dimensional graphics (3D).
2D graphics are used to do things like draw the user interface used by Windows XP or by a word processor. Drawing 2D graphics consists primarily of copying little prepared images to the screen, drawing characters from various fonts, and filling areas of the screens with a color. It's pretty basic stuff and even very old video cards are powerful enough to draw 2D graphics at lightning speed. If all you use is 2D graphics then just about any GPU will do.
3D graphics are used by games to allow you to move around within a virtual world. They're used by artwork programs to allow artists to design and view three dimensional models. 3D is also used by many engineering and architectural programs. Windows Vista is going to support a 3D user interface. Unlike 2D graphics, 3D graphics can require an enormous amount of computations. And however fast a GPU is at 3D, the image quality could be improved with even more processing power. Any old GPU can handle most 2D chores but you need to be careful to make sure that you get a GPU which is powerful enough for the 3D work it will be doing. And even if it's fast enough for your current 3D programs, new programs will be released in the future which will require even more 3D power.
Make sure to get at least a DirectX 9 video card. There's no point in buying a card from an earlier generation. There are some DirectX 7 and 8 video cards still available in the extreme low-end market but it's not a good idea to get them even if you have no interest in 3D graphics. DirectX 9 was the first version to ship with shaders which are flexible enough to serve most 3D purposes. Shaders are the programmable parts of GPUs. The DirectX 9 shaders make it less likely that you will have compatibility problems in the future. They've become the minimum expected feature set for an ever-increasing number of programs. At the low-cost end of the market, DirectX 9 cards are only slightly more expensive than the obsolete DirectX 7 and 8 cards.
When reading about GPUs you'll run into 3D terms like textures, geometry, pixel shaders, vertex shaders, shader models, etc. If you'd like to get a basic understanding of what those things mean then take a look at this page. It also gives a basic description of the capabilities of DirectX version 6 through version 10.
Microsoft's latest operating system is called Vista. Vista affects your choice of video cards because it comes with a new user interface called Aero. It's a 3D extravaganza of transparent gizmos, pulsing thingamajigs, and three dimensional whatchamacallits. Okay; you might see it differently. To me, it's a bunch of snazzy frills. But if you want those frills then you need to get the right kind of video card.
Lots of computers have video hardware which cannot run Aero so Microsoft includes an older basic user interface without the frills. All you need to run Vista without Aero is a video card with a DirectX 9 driver and at least 800 X 600 screen resolution. A video card can have a DirectX 9 driver without having support for any of the DirectX 9 features like pixel and vertex shaders. All that is required is that you can get a DirectX 9 compatible display driver for the video card. The hardware in just about any video card including ones designed for DirectX 7 and 8 is capable of running a DirectX 9 driver but the video card makers don't provide them for older video hardware. This page explains how to find the most recent display driver for a video card on the manufacturer's web site. If you can't get a DirectX 9 driver for the video card then it can't run Vista at all.
To run Aero, a video card must meet certain minimum hardware requirements. A video card must have at least shader model 2 pixel shaders. Those were originally introduced in late 2002 with the Radeon 9700 Pro. This means it must be a video card with hardware support for the pixel shaders in DirectX 9. Hardware support for vertex shaders is not required which is good news for folks with integrated graphics because most of them (notably Intel implementations) don't have hardware texture shaders. The video card must have 128 MB of video RAM. The video card is also required to support 32 bit pixels but I doubt there were ever any video cards made which had pixel shaders but didn't support 32 bit pixels. The video card must have a WDDM (windows display driver model) driver. This is a totally new driver specifically for Vista which works very differently than the old video drivers. If the video card's GPU maker (usually ATI or NVIDIA for video cards, Intel or VIA for integrated graphics) doesn't write a WDDM driver for the chip, then you can't run Aero on it. They will presumably write WDDM drivers for all GPUs which provide the hardware features needed by Aero. ATI Radeon 9500s and up have WDDM drivers. All Radeon X models (their newer PCI-Express cards) also have WDDM drivers. NVIDIA has WDDM support starting with the GeForce FX cards (GeForce 5s). All GeForce 6 and newer generations support WDDM.
Even if you meet Aero minimum requirements, it may not run at full speed when heavily loaded. Having more than 128 MB of video RAM is recommended. It's also recommended that you use a PCI-Express video card rather than an AGP or PCI card. PCI is not recommended for Aero because the PCI bus is very slow at transferring data between the video card and the motherboard. The latest version of AGP is sixteen times faster than PCI when writing data to the video card. That's more than fast enough for Aero. But many AGP implementations are only twice as fast as PCI when reading data from the video card and that's fairly slow. AGP is plenty fast for games because almost all of their data is written to the video card and they very rarely have to read from it. But Aero often swaps data back and forth between the motherboard and the video card so it needs both reads and writes to be fast. AGP is fast at writes but many AGP implementations are slow at reads. PCI-Express x16 slots can read from a video card at the same very fast speed it writes to it, so PCI-Express x16 is preferred for Aero. But it will work on AGP and PCI with somewhat reduced performance.
One of the decisions you have to make is how much video RAM is on the video card. The reason a video card has its own memory is for speed. A video card can access its own memory much faster than it can access memory on the motherboard. Video RAM is used to hold the most commonly accessed operands needed by the video card to draw its images. Less commonly used operands can be moved to the video card from the motherboard memory when needed. Having local video RAM on the video card makes things go much faster. If you don't run games (or plan to run Vista with the Aero user interface) then video card performance may not mean very much to you. But if you care about performance then having the right amount of video RAM is very important.
As of the end of 2006, you should avoid any video cards with less than 128 megabytes (MB) of video RAM. Any video card which has 64 MB or less is obsolete so there's other reasons to avoid them beyond the lack of video RAM. Vista Aero works best with 128 MB or more so it's becoming the minimum expected hardware on a video card. The Video RAM chips are so cheap that there's little cost benefit in going below 128 MB anyway. 64 MB cards are just obsolete video cards which someone is dumping. Avoid them!
If you're a gamer then getting the right amount of video RAM is very important. If there isn't enough video RAM to hold all of the commonly accessed operands then the performance suffers. Stuttering in games is a common symptom of having too little video RAM. While having too much video RAM doesn't hurt your gaming performance, it doesn't help it either. The video RAM holds things like textures (the images on the surfaces of 3D objects), geometry (the 3D points which determine the shape of objects), and frame buffers (copies of intermediate or final screen images). The GPU on a video card is capable of drawing at a certain speed. Faster GPUs can draw higher quality objects at higher resolutions. Higher quality objects require operands which take up more RAM space. So you need a rough match between the speed of the GPU and the amount of video RAM on the video card. If there's too little video RAM, then your GPU is capable of drawing higher quality objects then you can fit into video RAM. You either have to run lower image quality than your GPU can handle, or you use higher quality objects and store some of them in motherboard RAM and live with the stuttering. If there's too much video RAM then you can fit very high quality operands into the video RAM but your GPU isn't fast enough to draw them. When you have too much video RAM, your only practical option is to stick with the object quality which your GPU can handle and leave the rest of the video RAM unused. You can get an idea of the right amount of video RAM for a given GPU speed by checking the video card table. Most of the cards in a given speed range have the same amount of video RAM. If you see a video card which has half of the video RAM as similar speed cards then you should avoid it. If you see a card which has twice as much then you should take into account the fact that the extra video RAM will only occasionally help your gaming performance. Some video card manufacturers try to take advantage of people by selling extremely low-end video cards with excessive amounts of RAM. A common trick is to sell a video card with 512 MB which really can only effectively use 128 MB. People who don't know any better end up buying these "sucker" cards because the only number they understand is the amount of RAM and they think lots of RAM must mean extra speed. Be sure to avoid these cards. And if you ever meet one of the marketing weasles who decided to sell this kind of card, be sure to punch 'em!
There's more to 3D than just games. Artwork programs can have quite different video RAM utilization patterns than games. Some artwork programs run better with very large amounts of video RAM which would benefit games very little. If you intend to use a video card in that kind of program then check the program's recommended video card requirements. That will tell you if the program has any unusual video RAM requirements.
Another video RAM issue you have to consider is memory bandwidth. Memory bandwidth tells you how fast the video card can access its video RAM. It's very common to run into two similar video cards with the same amount of video RAM where one card's RAM has twice the bandwidth of the other card. This is especially common in low-end video cards. The video card with twice the memory bandwidth is usually just a little more expensive than the much slower one. The speed of the RAM comes from two things: the clock rate of the RAM, and the width of the RAM. The clock rate is how many times per second the RAM can be accessed. The width of the RAM is how many bits of RAM are accessed at the same time. Low-end video cards often come with either 64 bit wide video RAM or 128 bit wide RAM. The 128 bit video card accesses its RAM at twice the speed of the 64 bit video card. Low-end cards are often limited by the speed of their video RAM so it's important to avoid the smaller RAM widths if you care about speed. The bandwidth column in the video card table gives you the peak memory bandwidth for the various video cards. Many websites which sell video cards will list the video RAM width and clock rate so you can make sure you're not getting one of the half-speed video cards. Unfortunately, quite a bit of that information is inaccurate. This page gives a detailed explanation of memory bandwidth and things to watch out for.
As if you haven't got enough to worry about, there's one other thing to watch out for when it comes to video RAM. Some of it isn't real! Some low-end PCI-Express x16 video cards use motherboard RAM to augment RAM on the video card. It's a way to make extremely inexpensive video cards which cut back on RAM on the video card by borrowing RAM from the motherboard. The specifications for these video cards often refer to the motherboard RAM as if it were video RAM so I'll call it "fake" video RAM to distinguish it from "real" video RAM which is actually on the video card. NVIDIA's implementation is called TurboCache and ATI's is called HyperMemory. The problem is that video cards can only access motherboard RAM very slowly. And almost all of the video cards which come with fake video RAM have 32 or 64 bit wide video RAM which means that it has extremely low memory bandwidth. You have to be a bit careful when buying low-end video cards because some models of the same video card use fake video RAM while others use only real video RAM. For example, there are various models of the NVIDIA GeForce 6200. Some models use TurboCache and some models don't. And the ones which do use TurboCache usually emphasize the amount of fake RAM and not the amount of real RAM. If you see a video card which is advertized as "Geforce 6200TC supporting 256MB(64MB on board ) 64-bit", that means that it has 256 MB of fake video RAM (the "TC" is for TurboCache), 64 MB of real video RAM, and the video RAM is 64 bits wide. The RAM size column in the video card table distinguishes between real video RAM and fake RAM but you need to be careful when purchasing a card which may have fake RAM. As long as you understand the real performance of these video cards (which is usually quite low) they can be acceptable choices for some people. Just don't let the impressive sounding amount of fake video RAM fool you. Almost all of these cards are extreme low-end hardware.
When buying a video card, one of the things you have to watch out for is low-profile cases. Many large computer makers (like Dell, HP, etc.) make some computers which use small cases. The problem with these cases is that standard video cards are too tall to fit inside. The top video card shown above is a standard-height card. The bottom card is a low-profile card. The vast majority of video cards are standard-height cards. The large piece of metal at the back of a video card (shown here on the left) is called the rear metal bracket. Rear metal brackets are bent 90 degrees at the top so they can rest on part of the case. A screw usually holds down the top of the rear metal bracket so the video card doesn't come loose.
The image above shows a low-profile case on the left and a standard-height case on the right. It should be fairly apparent which kind of case you've got. If not, then take the measurement shown with red arrows. It's the distance from the motherboard to the top of the rear metal bracket. For low-profile cases the measurement is about 2.83 inches (72 millimeters). For standard-height cases the measurement is 4.29 inches (109 millimeters).
If you have a low-profile case then you'll have to shop around to find low-profile video cards. They're not very common. Most low-profile video cards are low-end cards so you'll have a hard time finding a fast one. You also need to be careful about the video RAM width. Low-profile video cards are often the models which have small video RAM widths. It's very common for the standard-height version of a particular video card to have full width video RAM while the low-profile version has half width RAM which seriously hurts performance. If you need a low-profile video card but would like decent performance then you're going to have to be extremely careful not to end up with one of the half width RAM video cards.
Then you have to deal with the rear metal brackets. There are a few low-profile video cards which come with the low-profile rear metal bracket. But there is a wider selection of video cards with standard-height rear metal brackets which have circuit boards which are short enough to fit into a low-profile case. If you get one of those then you can unscrew a couple of screws, remove the standard-height bracket, and then insert the video card into the case without any bracket. You can't screw the card into the case but it will stay in the slot as long as you don't move the computer or pull on the monitor cable. Or, if you're capable of some basic metal work, you can cut and bend a standard-height metal bracket to be the same height as a low-profile bracket.
Since low-profile cases also tend to only accept short expansion cards, it's a good idea to check the length of the video card to make sure it will fit. Some video card manufacturers list the size of their video cards on their web sites. If not, then you can get a good approximation of the video card's length by checking the pictures of the video card at Internet vendors like newegg.
If you want to do yourself a favor then avoid buying low-profile cases in the first place. They put serious restrictions on your expansion ability and you can get plenty of small cases which can still hold standard-height expansion cards.
If you have a small standard-height case and are looking at a large video card then you should make sure that the video card isn't too long to fit in the case. Sometimes you can't fit a long video card into some smaller cases because the hard disks or optical drives at the front of the case get in the way. Long video cards can also block motherboard connectors for hard disks, floppies, etc. High-end motherboards usually have layouts which take long video cards into account so things aren't usually blocked. But the size and design of the case can also prevent you from adding some of the larger video cards. If you have a full size ATX case, then you can usually fit any video card into it as long as you're willing to temporarily remove some hard disks, sticks of RAM, or cables from the motherboard while you're installing the card. Sometimes, it can be a bit of a puzzle to figure out the right component installation order to get everything to fit. Of course, if you just buy large cases you can avoid the problem entirely.
Most video cards get hot enough that they require fans blowing over a heatsink to cool some of the silicon chips. If the chips get too hot then the video card can malfunction or even be permanently damaged. Generally speaking, faster video cards get hotter and require bigger fans and heatsinks to stay cool. The max watts field in the big fat video card table shows the approximate power consumption of many video cards. The video card shown above in the middle consumes so little power that it doesn't need a fan at all. Many low-end video cards and some faster ones come with passive cooling which means that there is no fan. That's very useful if you want to build a quiet machine. You still need some air circulating through the PC's case to keep such cards from overheating but that's easy to do very quietly. Another benefit of passive cooling is that you don't have to worry about the fan dying. Fans are the part of the video card which is most likely to break. Some higher-end video cards use so much power that they come with large heatsinks which make the card very thick. Those kinds of cards are often wide enough to block the next expansion slot expansion slot over on the motherboard. The video card on the left takes up two expansion slots. When getting that kind of video card, be sure that you'll still have enough expansion slots after inserting the video card. It's easy to run out when your video card is using two expansion slots.
The video card is a source of heat in the computer. High-end video cards can be the main source of heat generated in the computer. The chips on the video card must stay below a given temperature to work properly. With normal video card cooling as shown in the center and right video cards, the heat from the video card is generated inside the case. If there isn't enough air flowing through your case then the insides of the machine will get progressively hotter. If you're moving from a low power video system to a high powered one then you may need to upgrade your case's cooling. Many of the extra-wide video cards which take up two expansion slots have cooling systems which expel their heat out the back of the computer. You can see the air holes in the rear metal bracket where the warmed air comes out. This is a very effective design at keeping the inside of your computer cool despite adding a high-powered video card. Some of the extra-wide coolers only blow half of their hot air out the back of the computer and exhaust the other half inside the case so you have to look carefully at pictures of the card to tell which design you have.
It's not that easy to know whether you need to upgrade your case cooling before you've installed the new video card. The easiest thing to do is monitor the case temperature and then add an extra fan to your case if you need one. Most current computers have a program which can monitor the temperature inside the case so you can see if it's gone up very much. If your computer didn't come with one then you can try utilities like SpeedFan or SensorsView. Of course, a thermometer left inside the case will also do the trick. A few degrees centrigrate increase probably won't matter but 10 or 20 probably means you need more (or faster) fans. Most cases use fairly standardized fan sizes and connectors so it's relatively easy to substitute higher speed fans. You can get fans from most internet vendors who sell computer components.
If you're a serious computer gamer, your video card just can't be fast enough. No matter how quick your machine is, some game developer will eventually come out with a new title which brings your computer to its knees. The video card companies announce their extreme high-end US$600 solutions to dwindling frame rates with the fanfare normally reserved for celebrity weddings. Video card designers constantly strive to find better ways to give gamers that top-of-the-line rush that comes from having the fastest video card in your virtual neighborhood. And yet, it's never enough. Why spend a mere $600 on your video system when you can spend $1200 on one that's occasionally twice as fast? Well, they've found a way to do it. NVIDIA's version is called SLI and ATI's is called CrossFire. SLI and CrossFire allow two video cards to work in tandem on the same game to increase the performance. It only goes twice as fast in the best of circumstances. Those circumstances arise often enough to satisfy many deep-pocketed gamers. You can check out the performance of SLI and CrossFire rigs on many gamer oriented pages. One of the advantages of the ability to run two video cards in tandem is that you can build a computer and only buy one video card to start with. Then a year or so later you can buy another copy of the same video card (at a much lower price) to give your machine a performance boost. Or, sometimes it makes more sense to sell your old video card and get a new one to replace it. The ability to run them in tandem gives you the option to go either way.
SLI and CrossFire work only with PCI-Express motherboards. The motherboards have two PCI-Express x16 slots and provide other special hardware to support running the video cards in tandem. You also need a powerful power supply if you're going to use two high-power video cards. Basically, you need a computer specifically designed to support running in tandem. As of the end of 2006, there are motherboards which support SLI and motherboards which support CrossFire but no motherboards which support both. You have to choose ATI or NVIDIA when you decide to run 'em in pairs. A serious dissertation on the subject of SLI and CrossFire is beyond the scope of this page. Besides, if you're seriously considering building such a rig you'll want to spent some time reading the "gee-whiz" details of the subject so you can look forward to having the fastest gaming computer in existance. These pages give you the technology basics on NVIDIA's SLI and ATI's CrossFire. Then you can see both of them in initial action here and here. Once you're done with those you'll be able to find SLI and CrossFire systems in most gamer-oriented benchmarks.
If you're looking for improved gaming performance then keep in mind that adding a high-end video card to a computer with a low-end CPU isn't going to turn it into a serious gaming rig. Your CPU has to do quite a lot of work to keep your video card fed with data. Running games with higher image quality requires not just a fast video card, but a fast CPU as well. Some games don't load your not-so-fast CPU very much and will benefit from a mismatched video card upgrade. But lots of games assume that there's a rough match between your CPU speed and video card speed. If you try to run a game with high image quality settings then the CPU overhead goes up. No matter what kind of CPU you have, a faster video card will allow you to increase the screen resolution and enable things which increase image quality like anti-aliasing. But once you start trying to run a game which has lots of different of objects on the screen at once, your old, slow CPU will start bogging down and the video card will spend time waiting for your CPU to get things done. When DirectX 10 comes along (and most games start using it which will probably be years later) then the amount of work your CPU has to do to keep the video card busy will go down substantially. But with DirectX 9 or earlier, your CPU has to do a lot of work to keep your video card speeding along.
So if you've got an older computer, it's a good idea to check the general gaming speed of your CPU and make sure you don't waste money on a super high-end video card which will be limited by your CPU. This page gives a general rating of CPU gaming performance. If you have a low-end CPU then you'll only get limited benefits by getting a high-end video card.
This page contains a list of most common video cards and a summary of their technical specifications. For the gamers out there, the list is sorted (approximately) from fastest to slowest in gaming performance. If you want detailed but concise information about a wide range of video cards, then the big fat table of video cards is a good place to spend some time.
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Copyright © 2005 through 2007 by Mark Allen