Re: Dual monitor PCI Express video cards

In article <nospam-1003062210290001@xxxxxxxxxxxxx>, Paul says...

In article <dut1a50fug@xxxxxxxxxxxxxxx>, Patrick Flaherty
<Patrick_member@xxxxxxxxxxx> wrote:

Hi,

My first home-built was 2 yrs ago. Athlon XP 2000+ (1.5 GHz), Asus A7N8X-E
mobo, gig of memory, etc. Big improvement on the 1GHz Pentium (Pentium Pro
even?) machine that my company had given me for a home machine. (plus
this one I owned).

Getting a little long in the tooth, and much as occurred between.

Thinking about an Athlon 64 X2 of some kind. This means PCI Express and
I have to get a new video card.

Problem is, I use dual monitors. Currently 2 17" NECs I believe (I'm at work
now). They have DVI (in addition to analog) connectors on the back.

Dual monitor PCI (x16) Express cards?

The least expensive thing (I'm not a gamer [but I am a big multi-tasker, hence
the dual core]) I find on NewEgg is:

http://www.newegg.com/Product/Product.asp?Item=N82E16814102664

An ATI. But I'm confused. The problem with less expensive dual DVI PCI Ex
cards is that they all have a max resolution of 2048 X 1536.
2 times 1024 X 768 that is. But my second (and last) requirement.
1280 X 1024 (or better) resolution.

The confusing part (with the ATI card) it says its 'normal' max resolution is
the same (insufficient) 2048 X 1536. BUT, if you use something called 'dual
line2' then the resolution can go up to 3840 x 2400.

What's dual link2? Look around. It's DVI but will all the pins populated and
two, parallel 'links'. I guess doubling the amount of pixels you can get
to the screen.

Looked at what I'm working on here at work (dual mon; AGP; DVI). The
female DVI inside the monitor is fully populated with pins. However
the male connector
coming from the (AGP) video card is 'half-populated' (single link).

And yet the monitor is doing 1280 X 1024.

But this is AGP. And maybe this is a difference between ABG and the
PCI Express 16 card that I would need to buy for my proposed machine.

So if 'dual link2' just a matter of making sure that the DVI on the back
of your monitor (monitors in my case) is fully populated (with pins)
AND the cable of course.

And a general explanation (if someone feels so inclined) of dual monitor
considerations in PCI Express vs. AGP would be very helpful.

Hope someone can explain this to me (and yes of course, I'm looking around
for Web pages that would do the same).

pat

Output limitations on video cards, are rated in terms of bandwidth.
You are talking about taking a virtual 2560x1024 desktop, and arranging
it on two outputs. Each output only has to run at 1280x1024 in this
case, so a cheap video card with two connectors on it will do the
job. In other words, you don't need a FireGL for this application,
and a $50 video card can probably do this.

The virtual desktop is constrained on the video card, by the video
RAM. Even cheap cards have a good quantity of RAM that can be used
for a frame buffer, so they don't even wince when asked to hold the
2560x1024 test case.

The video card has either a VGA (analog only) connector, or a
DVI-I analog plus digital connector is the other common type.
(Occasionally you might find a DVI-D digital only, so it pays
to ask.) The DVI-I can be single link DVI or dual link DVI
digital output.

The VGA output limits are determined by the RAMDAC bandwidth.
A 400MHz RAMDAC apparently can draw a 2048x1536 pixels, at some
refresh rate like maybe 60Hz. With two VGA monitors connected,
the virtual desktop is 4096x1536 max. Output PI filter limitations,
cable limitations, and monitor limitations, make this 2048x1536
kinda hard to achieve, with crisp quality, but you can still dream.
That is why at some point, it pays to switch over to digital output.

For DVI, see this article:

http://en.wikipedia.org/wiki/Dual-link_DVI

A single link DVI (the most commonly encountered kind), works
at up to 1920x1200 @ 60Hz digital, with reduced blanking. If a
CRT had a DVI interface on it, it would likely not like reduced
blanking, but a fully digital display subsystem like an LCD
doesn't really care about blanking, because there is no "flyback
time" or "retrace" on an LCD.

A dual link DVI (moderate to high end cards, hard to find, and
hard to be sure you have got it), can do 2560x1600 at somewhere
close to 60Hz. You may find cards with only one dual link
connector, or perhaps a high end card with two dual link
connectors. In principle, that means up to 5120x1600 virtual
desktop.

AFAIK, the 3840x2400 is the top resolution that you might find
commercially. In several cheap ATI video card manuals, ATI claims
they have done 3840x2400 @ 15Hz on a single link DVI connector,
without hardware modifications. In other words, they trade a
reduced refresh rate for increased spatial resolution. Such a
display would run like a slide show.

With a dual link interface, that means you could likely do the
same thing at 3840x2400 at 30Hz. You could do a bit more than
30 Hz, if the TMDS transmitters could be bumped from 165MHz max
to 180MHz+. So perhaps a bit more than 30Hz refresh can be
accomplished, assuming that the monitor can actually be
refreshed faster. As with analog output, digital has its limits
too, and a cheap TMDS transmitter might not work well at 165MHz,
or the cables might cause your display to be "snowy" due to
tranmission/data clocking errors.

More info on the T221, which started the large monitor madness,
is here:

http://en.wikipedia.org/wiki/T221

In terms of the gaming industry, Matrox may have disappeared
from sight as a high end gamer, but they have decided to pick up
the bread crumbs left lying around by their competitors. For
example, this quad output video card allows four LCD monitors
to be driven. Such a solution would be acceptable for 2D graphics
or stock trading, where a lot of information must be displayed
at the same time. Everything they make these days, seems to be
strange in one way or another...

http://www.matrox.com/mga/pid/products/qid_lp_pcie.cfm

HTH,
Paul

Hi Paul

Thanx. Lot of info there. I'll have to go over that a couple of times before I
absorb most of it.

I think though ... one import of what you're saying (and contrary to my earlier
understanding). It would suit my needs just fine (2 monitors with a 2560 X 1024
virtual desktop) to get a 2-DVI (DVI-I) card where the max resolution (I'm
looking mostly at NewEgg) is rated at 2048X1536 because ...

This is the max rez PER MONITOR.

Is that correct? I (obviously) was assuming that the max rez was that when
stretched out over both monitors.

In which case the following (the cheapest 2-DVI PCI Express 16 card on NewEgg)
would do what I need:

http://www.newegg.com/Product/Product.asp?Item=N82E16814131426

thanx for your help.

pat

.

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