clarify for me 32bit data bus?

[diurnal]

I recently played this game namely Deus Ex and the graphics were terrible.
So I was wondering if the 32bit databus and external bus was the culprit. I know the new playstation 2 is 128bit and the graphics are ausome. Also every time i look at video cards they say it is 128 bit 3d graphics however is the graphics bottlenecked by the 32 bit data and external bus?So are video card manufaturers lying when they say 128 bit when you can only run 32 bit? Thnks

[yawningdog]

Your questions are too numerous and sundry for me to get them all, but I think I can explain what a data bus is.

Think of data as sand in a sandbox. For every 8 bits in the bus, you have a shovel. For a 32 bit bus, four shovels are moving sand in and out of the sandbox. A 128 bit bus moves sand 16 shovelfuls at a time. So, yes, a bottleneck is created by the external bus, but this doesn't necessarily account for lousy graphics. No, I don't think it can be said that the video card manufacturers are lying (about the data bus. I'm sure they lie about other stuff.)

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He thrusts his fists against the posts but still insists he sees the ghosts.

[wolfmann1]

Its the core technology and drivers that are probably the culprit...running a 4mb Voodoo card probably isn't advisable, as I have a TNT2 32mb card on a P3 450 and it gets choppy, especially when you look up at "the Lady" in Deus Ex. There is a Direct3D patch to help fix that, but if you're using 3Dfx card, Glide should make it run very very fast. But remember, Voodoo is almost six years old now...be lucky you can even play it, if you have that 3D card.

Anyway, back to the 32-bit thing. 32-bit in video cards is one of two things 1) bus width) and 2) color depth.

I'll explain the first

1) The above sandbox analogy is correct, but kinda of confusing. When I compare processing power and bit rate I always go with a river, because a river flows in a direction and is easy to relate to.

Take an average river that is 16-bits wide, or 16 meters wide. The water is flowing through it at 33 meters per second, or let's say 33 megahertz per second. The water (or data) is moving at a constant rate of 528 mega-feet per second (16x33). Widen the river to 32-bits, with the same 33mhz speed, and now you have effectively doubled your throughput, bandwidth, or the amount of water going through it. Increase the speed of the river and while the same amount of information can go through it, it goes through faster. You get more information through, just because more information can be processed at one time. At the same speeds, 32-bits will be faster than 16-bits...theoretically. However, with small bit rates you can scale to faster speeds without data integrity loss. That is how a 16-bit bus could outperform a 32-bit bus. Depends entirely on your application.

You hit a practical limit around 128-bits where data integrity is compromised and you have to slow the information passing through. Most chipset and memory controllers on modern video cards are 128-bits wide, even if they say they're 256-bits wide, they really aren't, they are simply using two 128-bit pipelines. Matrox G400 Max's do this, for example, and so does the GeForce series of cards...in fact they use four pipelines. The GeForce3 I believe uses even more, because it ran render about 8 textures in one pass, and you need at least one pipeline per texture if you're rendering it at the same moment. Don't worry about that, it isn't required information.

But that doesn't really matter, because the video card maybe able to process information 128-bits at a time, but it is still hampered by the system and AGP bus which is only 32-bits wide.

So think of bit depth as the width of the river, or the width of the data doing through it, and remember that wider is better, generally, however if the data going through it isn't fast enough then it doesn't matter.

2) Color depth is dependent on what your graphics card can output, and below 16-bit will severely affect graphics quality in colors, at least. Anything at 16-bits and above is negligible, but is noticeable on really good image quality cards like ATI or Matrox cards. All graphics card can manage 256 colors, or about 8-bit color. Most to all of the graphics card on the market are able to produce 16-bit (65,553 colors), 24-bit color (about 13 million colors), or 32-bit color (about 16 million). 24-bit and 32-bit colors actually don't display any more colors per se. 32-bit color simply has an extra 8 alpha, or transparency channels. So all your 13 million colors can now have different shades of transparency...think of it like looking through stained glass...there are an extra 3 million colors which have different transparency levels.

As for the Playstation 2 having awesome graphics, that is simply a result of the core technology being very strong and good...but to be honest with you, wait until the X-Box comes out with Nvidia GeForce 3 based programmable shaders...Playstation 2 is going to seem...out dated.

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