How Your Video Card Works & Common Video Card Myths

[zSilverFox]

Two things I wrote a few weeks ago. Enjoy.

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I've seen all too many people ask why having X amount of RAM on Y card for playing Z game is overkill or underkill, or just having no idea how cards work. So... here's a little guide for ye all. My source is the nVidia GPU Programming Guide, so it may be a tad bit different for ATI cards. Accurate as of 7/08/05.


Ok, first, your CPU sends data to your video card to be cached in RAM. This is what it's there for, to hold pre and post-processed data.

Next, Geometry and Commands are sent to the Pre-T&L Cache. Vertex Shading (T&L) then takes place, and the data is sent to the Post-T&L Cache. Then, this data is sent to Triangle Setup and Rasterization.

Now, what about Textures? They're sent to the... take a guess... Texture Cache. Fragment Shading and Raster Operations are then executed on those Textures and semi-processed Geometry from the Triangle Setup and Rasterization stages.

All this is then sent to the frame buffer, which is located within your VRAM. Now what? The RAMDAC sends this info out through your VGA/DVI port, and the rest is for another guide.


That's the basic overview of how at least an nVidia card works. I would love it if this were pinned, but I doubt that'll happen.


And now, an FAQ:

Q: How much VRAM should I have to play Doom 3? BattleField 2? Half-Life 2? Quake?

A: While Quake runs just fine on 64 megs of VRAM, at least 128 megs of VRAM should be used if you wish to smoothly play games such as Doom 3, BattleField 2, and Half-Life 2 (Which will be referred to as D3, BF2, and HL2 respectively from now on) at medium to high texture settings on most maps. 256 megs will allow you to play a bit more smoothly at higher settings, due to having more RAM to cache all the raw data in.

Q: Why are there cards with 512 megabytes, or even 640 megabytes of RAM then?

These cards are usually workstation cards. A workstation is usually a very high end computer used to make money. Most are for high end A/V work, CAD, etc. You'll usually see $10k+ applications on these machines. Cards with these huge amounts of RAM usually run on Quadro or Realizm cores, and will cost you a VERY pretty penny or two. Two Quadros in SLI is a scene you'll find in many a high end workstation, where millions of poly's are being rendered every second.

Q: What's this SLI you speak of?

A:

Quote:

Originally Posted by nVidia

An NVIDIA SLI system includes a PCI Express motherboard that supports two physical connectors that are capable of having two NVIDIA-based PCI Express graphics cards plugged into them. Joined by the NVIDIA SLI connector, the two graphics cards power one monitor, delivering earth-shattering PC performance. Screenshot courtesy of 3DMARK03.

**The NVIDIA SLI connector is only used with GeForce 6600 GT products and above.

Basically, it allows you to use two PCI-E x16 cards (both running at x8) to process data at the same time. The work load is divided among the two at either 60/40, or X/Y axise.

For ATI cards, there's another technology called Crossfire.

Q: What's Crossfire?

A:

Quote:

Originally Posted by ATI

To build your own latest generation multi-GPU system, start with any existing Radeon® X800 or Radeon® X850 graphics card and a CrossFire Ready motherboard, such as those based on the ATI Radeon® Xpress 200 CrossFire chipset. Then add a Radeon CrossFire Edition co-processor board and plug in the external cable to unite multi-GPU power.

[towlies high]

i say it should be pinned, good write-up

[zSilverFox]

Thanks. And here's another little thing that I wrote last night.

Quote:

A Guide to Video Card Lingo

Enjoy .

Accelerated Graphics Port (AGP)
An interface designed specifically for video cards. It has four bandwidth options for sending and recieving information from the CPU, which are 1x, 2x, 4x, and 8x. Most AGP cards are 8x, and are backwards compatible with older motherboards that support 4x at the most.

Alternate Frame Rendering (AFR)
Rendering mode used by ATI's Crossfire technology.

Anisotropic Filtering (AF)
Anisotropic filtering is a method of making textures look sharper, or less blurred. There are varying levels of AF, which define how many samples are used by the algorithm, which are 2x, 4x, 8x, and 16x.

Anti-Aliasing (AA)
Anti-Aliasing is a set of algorithms that get rid of aliased, or jagged edges. Like AF, AA has varying levels of samples, which result in finer edges, which are 2x, 4x, and 8x in some higher end cards. AA can substantially cut down on your frame rate or FPS, depending on how many pixel pipelines there are and the CPU Bottleneck (both of which will be defined later)

Artifact
An artifact is a poorly rendered or sub-rendered texture or polygon, usually resulting from too high of an overclock on the GPU, or an unstable pipeline unlock.

Benching
The act of running a benchmark.

Benchmark
A score or program (Such as Aquamark or 3DMark) that's used to compare the power and ability of a card to others. The most common GPU benchmarking program series is 3DMark, by Futuremark. Futuremark offers free versions of each of their products, with the option to purchase them in order to gain access to more power or features.

BIOS
Basic Input/Output System. It's usually changed by enthusiasts with cards with locked, or disabled pipelines, to unlock or re-enable them.

Bottleneck
A bottleneck is something that will decrease the performance of a product. With video cards, the two biggest bottlenecks are CPU speed and amount of RAM. To eliminate or substantially decrease a bottleneck, you can increase the speed of your CPU and amount of RAM in your system.

Bus
System of wires or traces through which information is transferred.

Card
See Graphics Processing Unit

Crossfire
A multi-GPU system developed by ATI Technologies Inc. It allows a user to use two cards for frame rendering. To take advantage of Crossfire, you must purchase a Crossfire Ready motherboard (such as the RX200 by DFI), a Crossfire Master Card that supports the specific series of card you wish to use, and a card that's supported by that specific master card. For example, if you wanted two X800s, you would need to buy a Crossfire X850 or X800 master card, and a standard X800(GT, GTO, XL, XT, XT PE) card, or a lower card.

Crossfire Master Card
A video card without a standard BIOS, used for Crossfire systems.

Digital Imaging
Computer aided photo editing and creation.

Frame
One "snapshot" or amount of data that has been rendered and is ready to be displayed onscreen.

Frame Rate/Frames Per Second (FPS)
The amount of frames a specific card can render per second. Most gamers prefer at least 30 FPS, while a large amount prefer at least 60 FPS, and so on.

Graphics Engine
A software program or set of algorithms that handles most of the software level graphics work for an application.

Graphical Processing Unit (GPU)
Like a CPU for graphics, it's the core chip of a graphics card. It handles all calculations regarding an algorithm, and directs the hardware inside of it.

High Dynamic Range (HDR)
A lighting and shading algorithm used exclusively in nVidia cards and the ATI X1 series. It enhances the lighting and shading of a frame immensely. Currently, the only graphics/game engines to make use of it are the Serious 2 engine, Source engine, and the FarCry engine.

High End Card
Term used to refer to the best card currently available, or a card among the best, such as the 7800GTX.

Low End Card
Term used to refer to a lower quality video card, such as the 6200.

Memory
Chips used for storage of pre & post rendered information and textures. Most cards have either 128 megabytes of memory, or 256 megabytes of memory. Common forms of memory are DDR, DDR3, GDDR2, and GDDR3

Mid Range Card
Term used to refer to a card inbetween the low and high ends, such as the 6600GT or 6800GS.

Peripheral Component Interconnect (PCI)
A 32 bit interface used by older video cards.

Peripheral Component Interconnect Express (PCI Express or PCI-E)
A PCI interface that has 16 lines of bandwidth for data transfer from the card to the CPU. All video cards after the X850XT PE and 6800 Ultra are PCI-E. PCI-E is also used for Crossfire and SLI.

Pixel Pipeline
A pixel pipeline can be viewed as an artisan or worker. It helps to handle the workload of a frame, therefor allowing it to be rendered faster. Pipelines are usually bunched up into "pipeline quads", which are groups of four pipelines, sometimes all of which handle the same specific or the same general job. A list of cards and the amount of pipelines in them:

nVidia/ATI
6200/X300-X600XT-X1300 Line: 4 Pipelines.
6600-6600GT/9800-X800GT-X700Pro X700XT: 8 Pipelines.
6800-6800GS/X800GTO-X800-x800pro-x850pro-x1600 line: 12 Pipelines.
6800GT-7800GS/X800X<->X800XTPE: 16 Pipelines.
7800GT/na: 20 Pipelines.
7800GTX/X1800XT PE (Not Yet Released): 24 Pipelines.

RAMDAC
Random Access Memory Digital-to-Analog Converter. It converts, you guessed it, digital signals into analog signals for VGA monitors.

Scalable Link Interface (SLI)
A multi-GPU technology system used by nVidia. It requires two identical cards be used on an SLI supporting board, with an SLI "clip." Also, SLI does not work on apps that do not have an SLI Profile.

SLI Profile
File used for SLI support.

Unlocking Pipelines
Unlocking pixel pipelines or vertex shaders on a card. It's commonly done with a BIOS flash.

Vertex Shader
Like a Pixel Pipeline, a vertex shader (vert for short) handles the shading of vertexes, or how textures and faces will look after rendering.


And now, I'm about to fall over from lack of sleep. Hope this helps with some questions, I'll edit in more info as words are thrown at me.

[ShuckyD]

STICKY anyone... nice job

[zSilverFox]

Thanks .

Added more onto the HDR part.

[wera]

STICKY STICKY STICK .

[pjaj]

Araldite, super glue, Evostick!!!

[Saico]

Myth: Crossfire works sort of like SLI, just throw in two (matched) cards.

Fact: You need a Crossfire master card for Crossfire, along with a board with the RX200 chipset.


thats sort of tru. several crossfire setups now work with matched cards, not a master and slave card. for example 2 x1300 or 2 x1600 dont need a master card.