How to choose a video card (2D & 3D) (preliminary!)
  
Proceed to the
January 1998 Video Roundup for 2D and 3D performance comparisons of today's most
popular chipsets, as well as visual quality assessments and links to individual reviews.
Or choose a review of an individual video card:
Introduction
Your video card is without a doubt one of the most crucial components of your system.
It provides the visual link between you and the computer.
Recently, the pace of innovation in the traditional 2D Windows acceleration field has
slowed, but manufacturers have now shifted their focus to the realm of 3D acceleration.
Make no mistake, new developments in the video card industry are as rapid as
they've ever been.
Driver support
The drivers for your video card are essential to making that card something you can
actually use. Good companies will continue to provide you with frequent driver
updates that resolve problems, improve performance, and provide more features. Bad
companies will leave you out in the cold trying to scrape enough money together to buy
another company's video card.
Of course, you still have to worry about whether your card manufacturer is responsible
enough to provide you with drivers for all the operating systems you might like to run.
Many companies, for example, allow their Windows NT support to lag behind their 95
support. Perhaps you would like to run OS/2, but don't have the drivers? The
feature set of drivers in these "alternative" OS's can also lag behind the other
more popular OS's, to the point where you are frustrated that you even bought the product
in the first place.
Features
DOS performance
Once this actually meant something, but today it's been relegated to the backburner by
the dominance of Windows. The speed at which an application or, most likely, a game
is able to draw graphics on the screen in DOS is a measure of its performance.
Windows/2D acceleration
What is typically meant by 2D acceleration is the ability of your video card to
accelerate certain drawing operations, like drawing a window, moving it, scrolling though
a document, rotating a picture, etc. With a good 2D card, you will find that working
in Windows 95/NT (or other operating systems) is much faster and more responsive.
The speed at which your card could do this used to be the major point of differentiation
for companies, but not any more. Most cards are so fast now in 2D/Windows
acceleration that the speed at which a card can do this is not as relevant as it used to
be. Almost every card is fast enough.
Video playback acceleration
Playing back videos on your computer can be pretty intensive on the processor, but the
real work comes when you have to change the size of the playback window or play back MPEG
video streams.
Most videos are smaller in resolution than your actual screen. Obviously,
watching a video in a tiny little window can be unpleasant and hard on the
eyes. A card that performs hardware scaling will allow you to blow the video
window up to full screen without slowing down the frame rate of the video tremendously.
Blowing up a lower resolution video to a higher resolution, however, means that each
pixel becomes bigger and more visible. Hence, the image can look blocky and
unrefined. However, if your video card can perform filtering on the video, each
pixel will be averaged with its neighbors to eliminate that blockiness and produce a
smoother and more natural looking image.
Most video cards on the market now are capable of accelerating MPEG-1 video streams so
that they will playback at full speed, and most can also resize the video with little or
no speed loss as well. In general, you don't really need to worry about video
acceleration much if you buy a modern video card.
A point of differentiation that is sure to come up in the future is the ability of your
video card to accelerate MPEG-2 stream playback. For most people, that means the
ability to playback DVD video. There is a whole lot of stuff involved in
accelerating MPEG-2 playback and I won't get into all of it here...but you should know
that few, if any, video cards can help accelerate MPEG-2 video today...most need help in
the form of an add-on card.
3D acceleration
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| Quake 2 - one of the most popular 3D accelerated games on the market |
This is the category where video card makers are concentrating all their efforts now,
and you can probably be pretty sure that it will continue to stay that way for a very long
time. You only need to lood at every game out on the market today to realize that 3D
acceleration is the way of the future for games and perhaps even applications, although
its usefuleness in that segment of the market still needs a little more definition.
Bilinear filtering
Let's say you have a texture of a certain size that you'd like to apply to a polygon.
What happens when you get too close to that polygon and the texture needs to be
blown up so that it covers almost all of your screen?
  
Without filtering, you can see the picture/texture become increasingly blocky and
pixelated. Now what bilinear filtering does is take a good guess at what pixels are
supposed to be there when the picture gets blown up by averaging together neighboring
pixels in the original texture. Here is the result.
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No bilinear filtering |
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Bilinear filtering enabled |
In most cases, this increases the amount of visual detail and makes the 3D scene more
pleasant to look at.
Note that the algorithm for bilinear filtering is not necessarily the same across all
cards/chipsets. Thus, it is possible for the filtering on two different cards to
look different. In most cases, however, you won't notice that much of a difference.
Mipmapping
Mipmaps are created for a number of reasons. First let's see what mipmaps are.
  
Let's say the original texture is the first and largest texture, 128x128 pixels in
size. The 3D accelerator creates smaller copies of this texture, 64x64, 32x32, etc.,
and stores them in memory as well. These copies are mipmaps.
Why is this done? Let's say you have a object very far in the distance with this
texture on it. Instead of having to load an entire copy of the 128x128 texture from
memory, the 3D accelerator can refer to a smaller precalculated mipmap like a 32x32 or
16x16 copy in order to conserve memory bandwidth.
The other reason has to do with the way 3D accelerators calculate the value of a pixel
far away in the distance. Let's say, for example, that the above texture is on a
square so far in the distance that it only takes up 4 pixels on your screen. In
order to properly calcalute the value of each pixel, the 3D accelerator would have to load
the entire 128x128 texture and average the whole thing down to just 4 pixels to display
the image correctly. In fact, many accelerators would simply take a few pixels out
of the original texture and average them together to get the value of a pixel in the
distance, creating an inaccurate representation of that pixel. A precalculated
mipmap has already preaveraged these pixels together, so that when the accelerator samples
a point it is actually working with pixels which represent what ought to show up at that
spot. This is quite hard to explain with words but maybe I'll be able to illustrate
with more pictures later.
You may have heard of trilinear mipmapping. You obviously can't have a mipmap for
every possible distance, so what trilinear mipmapping does is sample values from the two
closest appropriate mipmaps and average them together to obtain the value for the final
pixel.
Amount of RAM
Basically, the more RAM you have, the higher resolutions and color depths you can run
at.
Let's say, for example, that you want to run at a resolution of 1024x768 in 32-bit
color.
1024 x 768 x 32 bits = 25,165,824 bits
Now, at 8 bits per byte, you have:
25,165,824 bits = 3,145,728 bytes = about 3.2 MB
So you need at least 3.2MB of video memory to get a 1024x768 x 32-bit desktop on your
computer.
But since 2D and 3D are now being integrated on the same card, your video card needs
more RAM than ever. You will find that you not only need RAM to display the image on
the screen, you need more RAM to store all the textures for each 3D object, you need more
RAM to double buffer each screen for smooth playback, and you need more RAM to Z-buffer
objects for depth calculations. If you don't have enough RAM, you might find that a
game is thrashing the onboard texture memory and having to load textures from system
memory constantly, slowing your 3D accelerator to a crawl.
Type of RAM
EDO RAM
SGRAM
VRAM
WRAM
RAMDAC
This chip is what converts the digital representation of your screen stored in your
video card's RAM into a signal that your monitor can display on the screen. The
faster your RAMDAC is, the faster your screen can be refreshed and the easier on the eyes
looking at your monitor will be. The "DAC" in "RAMDAC" stands
for Digital to Analog Convertor. This is because the RAMDAC is converting the signal
from a digital representation of bits in your video card's RAM into an analog signal that
can be displayed on your monitor.
Because the RAMDAC is outputting an analog signal to the screen, you can't always
determine the visual quality of a RAMDAC from its MHz rating. In many cases, you
might have to rely on first-hand experience or word of mouth to figure out if the image is
acceptable for you.
AGP/PCI
What kind of slot do you want your graphics card to be in? AGP stands for
Accelerated Graphics Port. AGP 1.0 is basically a separate slot running at 66 MHz as
opposed to PCI's 33 MHz. Future revisions of AGP may support 2 or even 4 times the
current speed of AGP 1.0.
The primary reason that you want to put all that bandwidth on your video card is so
that you can lessen the impact of having to transfer textures from system memory when the
onboard memory of your 3D accelerator isn't large enough to store them all. Make no
mistake, however, AGP isn't a way to get around having more memory on your 3D accelerator.
Having more memory onboard is a much better way to do things.
So far, AGP has not proven itself to be of much benefit in 2D performance, although it
usually helps a little.
There is also another issue to consider...one which, were it not for the incredible
effect of 3Dfx on the PC 3D accelerator market, might not even be an issue. Because
the upcoming Voodoo 2 is expected to again raise the bar for 3D performance and will be
coming in AGP versions, you might want to opt for a PCI video card now and leave the AGP
slot open for an AGP Voodoo 2. Otherwise, you might end up having to get rid of your
AGP 2D/3D card when Voodoo 2 rolls around.
Performance
Proceed to the
January 1998 Video Roundup for 2D and 3D performance comparisons of today's most
popular chipsets, as well as visual quality assessments and links to individual reviews.
Overall, it's probably most important to remember that the major point of
differentiation in today's cards is in 3D performance, not 2D performance. It's
unlikely that you'll be dissatisfied with the 2D performance of any modern video card.
Summary
Richard Kuo,
rkuo@eniac.seas.upenn.edu
Last updated 06/02/98 08:33 PM -0400
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