Re: [gentoo-user] Running a USB graphics cards with Linux?

[Michael Mol <mikemol@gmail.com>]

On Tue, Jul 17, 2012 at 10:03 AM, Kilian Zott <kilian@diezotts.de> wrote:
> thats a strange comparison since usb is a serial bus
> vga is not even digital, so how can you talk about throughput? lol

Information doesn't need to be digital. Terms like 'bandwidth' really do apply.

VGA does place some structure on its signal. You have a vertical and
horizontal refresh rates. Your vertical refresh rate is usually in the
10s of Hz. I've seen displays range from 56Hz (terrible, terrible
flicker on CRTs) to 120Hz (smooth as glass). Your horizontal refresh
rates are usually in the 10s of *KHz*.

The combination of the two dictated how many scanlines you could fit
into your signal. Your number of pixels in a line was (in reality)
limited by your video card's dot clock, but you might adjust things if
you preferred, e.g. square pixels instead of whatever the per-pixel
aspect ratio normally was. (I really don't rememeber.)

Unlike DVI and HDMI, which support pixel formats that have
subsampling, VGA didn't have any kind of compression mechanism. You
had three channels, red, green and blue, and their voltage levels on
the wire controlled the brightness of that color at whatever
particular point on the display corresponded to that instant in your
horizontal and vertical sweeps.

If you'd like to know how I compare USB and VGA, look at ways VGA and
DVI are analogous. Of course, under certain (now very unusual)
circumstances, VGA can kick DVI's butt.

-- 
:wq