[rescue] Looking for 4 head AGP card (PeeCee)

nate at portents.com nate at portents.com
Mon Aug 13 10:27:37 CDT 2007

> I work in a Unigraphics shop so most of the workstations here are Dell
> Precision based.  Most have dual DVI outputs, a few of the oddball ones
> have
> a single connector that reminds me more of an HD-60 but wider, you have to
> use a Y cable to break the single connector out into dual DVI connections.
> Kind of weird but is this what you're talking about?

Dual-Link DVI has nothing at all to do with two physical DVI connectors.

DVI, based on the PanelLink serial format by Silicon Image, uses
Transition Minimized Differential Signaling (TMDS). A DVI link is four
twisted pairs of wires for red, green, blue, and clock used to transmit 24
bits per pixel, sent line by line with blanking intervals between each
line and each frame.  There's no packetization, compression or support for
only transmitting changed parts of the image, i.e. the entire image is
constantly sent all the time.  For each DVI link, max res at 60Hz is 2.75
megapixels. So for a 5:4 ratio at 60 Hz of you can have 1854x1483 res max,
or for 16:9 you can have 2212x1243 res max. Of course neither of those are
common resolutions - the closest down from each is 1800x1440 and
1920x1080, and for 4:3 it would be 1792x1344 or, below that, 1600x1200. 
In order to get higher resolutions, a DVI connector has the ability to
include a second DVI link, containing another set of red, green, and blue
twisted pairs.  With a second link active (which needs a dual-link video
card, dual-link DVI cable, and dual-link capable monitor) it allows
resolutions up to 4 megapixels at 60 Hz (alternatively, the second link
can be used to carry the least significant bits in a greater than 24 bit
per pixel image).

Some of you may now be wondering how single-link DVI can possibly do the
common 24" computer LCD 16:10 ratio of 1920x1200 at 60Hz, since that's
more bandwidth than the 165Mhz DVI spec can handle, and the answer is they
reduced the blanking interval in order to get the extra pixels across a
single DVI link.

- Nate

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