[CentOS] Centos laptop:: video cards

John R Pierce pierce at hogranch.com
Sun Oct 5 16:32:02 UTC 2014


On 10/5/2014 6:17 AM, Valeri Galtsev wrote:
> John, I would respectfully disagree. The bad thing about "shared" memory
> video cards is fundamental in the architecture. They use as video RAM a
> portion of main RAM, that means they place the video traffic (30, or 60,
> 50 25 frames per second multiplied by number of pixels worth) onto memory
> bus. This traffic has nothing to do with anything but the screen and just
> doesn't belong there. It is logically independent on anything and should
> be kept separate from memory bus - physically.
>
> I mentioned single board computer I soldered for my kid back then based on
> Z80 processor as an example of how rudimentary is to mix video traffic
> into memory bus. It was OK to do that on trivial amateurish single board
> computer. It is awful to step that low from architecturally good dedicated
> video ram away on modern sophisticated computer. My computer science
> degree rejects that and asks to take from "inventors" of that away their
> computer science degrees.

the Z80 had maybe 2MB/sec of memory bandwidth (thats off the top of my 
head before coffee).  A Z80 system rarely had over 64K of ram, usually 
static, btw..   the DDR3 on a Intel i5-4570 (random upper midrange cpu I 
picked) has 25.6GB/sec memory bandwidth.  a typical 1920x1080 display is 
2Mpixels, at 24 bit/pixel and 60Hz LCD refresh rate, thats 360MB/sec to 
refresh the display.  almost *nothing* compared with that 25GB/sec 
bandwidth.  lost in the noise (half of the .6, to be more specific).




-- 
john r pierce                                      37N 122W
somewhere on the middle of the left coast




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