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on-board video cardson-board video cardsPosted Sep 24, 2007 16:06 UTC (Mon) by giraffedata (subscriber, #1954)In reply to: on-board video cards by khim Parent article: What every programmer should know about memory, Part 1 I assume the performance sucking comes from the fact that the video controller is constantly reading from the memory to refresh the screen, even if no one is looking at it or no monitor is plugged in. Modern computers have power-saving features that disable the display after a period of no keyboard/mouse activity. Does that shut down the refresh in the video controller, thus eliminating the performance impact? What about DVI? VGA CRTs have to be refreshed constantly, from the video controller (and a VGA LCD monitor, emulating a CRT, would too), but what about DVI LCD display?
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on-board video cards Posted Sep 24, 2007 19:34 UTC (Mon) by khim (subscriber, #9252) [Link] DVI requires constant refresh too. It's not needed for modern LCD - that's just how DVI is designed. As for needless polling when monitor is power save mode... Few years ago it was certainly true anyway - but times are changing. May be latest integrated CPUs are stopping this useless polling when there are no need, I just don't know.
on-board video cards Posted Sep 28, 2007 14:41 UTC (Fri) by pm101 (guest, #3011) [Link] Are you sure?
My impression was that active matrix LCDs worked a lot like DRAM. They had a transistor and a capacitor for each pixel (the transistor was added in the move from passive to active matrix), but the voltage on that capacitor decayed and needed to be periodically refreshed. I was unaware of LCD displays having any on-board memory from which to do the refresh, but that could have been added while I wasn't following the market, although I'd be surprised, since it seems like it'd be an unnecessary cost item.
on-board video cards Posted Sep 29, 2007 21:49 UTC (Sat) by giraffedata (subscriber, #1954) [Link] It's not the physics, but the modernness that I think makes the refresh not necessary for LCDs at the level it is for CRTs: If I were designing a monitor in the 1990s out of parts that need to be refreshed (even a CRT), I would put required refresh function inside,rather than pass the responsibility off to the computer. In SVGA days, though, it probably made sense to keep the monitor dumb. But I guess DVI designers decided the computer wants to update the picture by a full raster scan 60 times a second anyway, so there's no need for internal refresh. Doing a little reading just now, it looks like the DVI data stream is a simple raster scan. It even apparently has "blanking intervals," though they couldn't possibly be for same purpose as on a CRT.
on-board video cards Posted Sep 29, 2007 23:06 UTC (Sat) by foom (subscriber, #14868) [Link] But I guess DVI designers decided the computer wants to update the picture by a full raster scan 60 times a second anyway, so there's no need for internal refresh. Doing a little reading just now, it looks like the DVI data stream is a simple raster scan. It even apparently has "blanking intervals," though they couldn't possibly be for same purpose as on a CRT. DVI's timing and blanking intervals are the same as VGA's. I believe it was designed this way to make the modification to the video cards easier, and to facilitate dual-output DVI / VGA video cards. (so the VGA port is basically just the DVI port with an extra D2A converter in the path.)
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