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# Memory Speed?

Posted on 2004-09-12
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With a display of 1280 by 1024 pixels & a refresh rate of 72 Hz, how do I find how fast the memory is?  I know the answer is 10 nanoseconds, but how do you get THAT?  I've looked everywhere & have found NOTHING.

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Question by:waxyice
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Expert Comment

ID: 12040580
I believe this would be the limitation of the chips used. I don’t know that there is a specific formula for taking the resolution and refresh rate to come up with the speed of the memory.
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Accepted Solution

complexymetron earned 500 total points
ID: 12040586
Hi!

Which memory? The one from the graphics card or the one from the display?
With the data provided you'll be able to calculate pixel clock (1280x1024x72/sec = 94.3 MHz).
If you're looking for the display's memory speed, you could just calculate: 1 / 94MHz = 10ns, which would match your questioned value.

If you're looking for the equation for the graphics card memory speed, there's an easy explanation for your failed search for information: it depends on what the manufacturer of the GPU designed into its chip. You can't tie the pixel clock to memory acces, becaus todays GPUs are capable of far more than just displaying pictures pixel by pixel.
They're able to calculate and transform complex 3-dimensional sceneries. So with every pixel you can see, there is far more information involved than just the color. BTW the fastest memory on graphics cards today is about 2.6 ns and even with that, GPUs aren't capable of delivering 72 frames per second all the time.

I hope I could clear things up a bit. If you're to confused, just ask again :)
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Expert Comment

ID: 12040605
Very cool, I had no idea :) I remember the days of calculating HOW MUCH memory you needed to display a res / color depth. God, am I old...lol
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Author Comment

ID: 12040626
Okay, just to see if I have the hang of it, see if this is correct...
with a display of 640 by 480 @ with a refresh rate of 60 Hz

640 x 480 x 60 = 18.4MHz

1/18.4 = 5ns?
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Author Comment

ID: 12040645
Opps, I did the final math wrong.  It would be 54 ns.
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Author Comment

ID: 12040650
Thanks you both for your help!  :)
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