Can someone explain Video Card memory to me?

[psy44]

Ok, I bought a new computer. The video portion was a 19" E90FB viewsonic and a ti 4200 w/128 mb AGP 8x. I thought that when you right click and get your display properties and you click the settings tab, under color palette I thought it would say 128 bit because there is 128 mb of ram, instead it said 32 bit. So basically I have two questions. First, How do I get higher bits (above 32, do I need a better monitor?)? Second, could you basically some up the purpose of video ram (in a simple way I can understand)?

 

[dullard]

I'll be as simple as possible.

1) Memory and color depth have nothing to do with each other. A video card can have any amount of memory, and it could use any size color palette, and they are completely unrelated. Note: A video card doesn't even need any memory, since they can be made to use your computer's memory instead...
2) More memory lets a video card do more complex tasks.
3) As far as I know no current video card does more than 32 bit color. So if you want more than 32 bits, be prepared to wait an extremely long time.
4) 32 bit color produces more colors than human eyes can distinguish between. So adding more colors would be a waste of time. In fact, the video card doesn't even use all 32 bits for color. A video card will calculate how much green/red/blue each pixel should display. If a video card used 8 bits for each color (or in other words one byte), there would be 24 bits used in the calculation for each color (8 per color times 3 colors). Each bit can have a value of 0 or 1, meaning there are two possible values for it. Thus a video card using 8 bits for each color will display 2^24 = 16.78 million colors. Humans can only distinguish between roughly 10 million colors, so already these cards are doing more work than we can see.
5) It uses the other bits to assist in the calculations - a video card running in 32 bit mode will have 8 extra bits to do its calculations with. The extra bits could be used for colors that no one can see; a silly thing to do. Instead it will be used to make the current video card's calculations more complex. Moving to 64 bits will give video cards a lot more room for pure calculations. However there is always a drawback. More bits = more work. More work means you either need (a) larger chips on the video card which adds significantly to their cost or (b) the video card is slower. If a card doesn't use the 64 bits, they go to waste, and you either have slower card or a more expensive card (depending on what the designers chose). For now, there isn't enough demand to warrant the move to 64 bits.

 

[Confused]

As dullard said, video card memory, and colour depth (the number of bits) have nothing in common.

This is hopefully going to be an OK way to explain video card memory (butchered slightly from my teachings on the CPU, and the internal memory on that)


All (modern) video cards have some memory onboard. This memory is used to store textures, player models, and any data that the graphics card might need in order to do it's job.
The onboard memory on the graphics card will be super quick. This means that it is really fast for the "core" of the card, the bit of it that does all the calculations etc, to access, and therefore makes the graphics card quick.
The amount of RAM on the card, determines how much stuff can be held. Textures in newer games are reaching like 70-80MB each, so of course it is useful for this to be able to be stored on the graphics card itself.
If the texture is bigger than the memory on the card itself, then it will use your normal system RAM.

Think of accessing the onboard video RAM as like walking to your fridge in the kitchen. From your bedroom (the "core"), it doesn't take long to go backwards and forwards to the fridge, which is just in the next room. Going to main system memory, however, is like walking half a mile to get to the local shops for the same thing.

If you have a fridge that can only hold 5 beers, then if you have to go to the shops often to stock up, but say your fridge holds 20 beers, then you have to go to the shops less often That's why more video card memory is useful


Hope that helps, and hasn't confused you too much!

Confused

 

[Lonyo]

32 bit colour is basically the most you can get. It's red/green/blue + alpha layer.
Each of the 3 colours has 8 bits to give a total of 256 different levels of the colout, 0 being no colour, 255 being full colour.
That gives 24 bit colour, the extra 8 bits to give 32 bit colour comes from the alpha layer which controls the transparency of the colour (whether you can see what's behind it or not)

It is related to video memory, and limited by it, but nowadays that has no effect, since it really was only an issue with cards having under 8MB Video RAM.