RE: Big LCDs

["Phil Harris" <phil@xxxxxxxxxxx>]

> -----Original Message-----
> From: ukha_d@xxxxxxx [mailto:ukha_d@xxxxxxx] On Behalf
> Of Neil Wrightson
> Sent: 28 April 2007 23:09
> To: ukha_d@xxxxxxx
> Subject: RE: [ukha_d] Big LCDs
>=20
> Hi Phil,
>=20
> Could you please elaborate on your below comment.
>=20
> All *WILL* require Dual Link DVI (not Dual DVI which is two DVI
> connectors)
> to realise their 2560 x 1600 resolution however if you do feed them
via
> single link they will generally display at 1280 x 800 pixels.

Never being one to shy away from the sound of my own voice then - if you
insist - yes.
=20
> Is there something different hear that I'm not up to speed on. I.e.
> 1) What is a "Dual Link DVI"

OK - The spec for a DVI connector has provision for two separate data
channels within one physical connector housing. The purpose being that for
"lower" resolutions only one channel is required to provide
enough bandwidt=
h
for the required resolution and refresh rate however as the required
resolution (and/or refresh rate) increases then the bandwidth required also
increases and becomes greater than that offered by that single data
channel=
.

If you look at DVI cables for sale you should see that they are described
a=
s
either "Single link" or "Dual link" which means that
they are physically
wired for either a single data channel or for dual data channels.=20

Offhand I seem to remember that a single link will handle something like
1980 x 1200 @ 60Hz (1920 x 1200 just sneaks in as being below that single
channel limit) whereas dual link will handle (again from memory so my
numbers might well be wrong) something like 2800 x 1600 - basically the
256=
0
x 1600 resolution of the big 30" LCDs sits within the specs for dual
link
DVI (but not by a huge amount IIRC) - there's not much leeway left in DVI.=
=20

> 2) Will one DVI only support up to 1280 * 800?

Nope - a single link DVI connection will support up to 1980 x 1200 (ish -
again, it's Sunday and I can't be fagged to look up the exact numbers). The
1280 x 800 resolution image that you get on the big 30"ers when
connected
via single link DVI is down to the fact that these big muthas generally
don't have *ANY* image manipulating circuitry built into them at all - they
have controls for on/off and brightness (as a function of the backlight
intensity) and that's about it. The controls for contrast, colour balance
and correction etc are handled by the graphics card. Because the displays
have no image processing built in then all they do is report back to the
source device that they are 1280 x 800 resolution when they get a single
link connection and simply pixel double that to give a full screen image
(yeuch!).

> 3) Do you need a video card with two DVI outputs?

No - this was my worry when I saw Chris' posting - that someone would think
it used two DVI outputs or required two DVI connections.

Basically a video card can have one or more outputs ... if one or more of
those outputs are DVI connectors then those DVI connectors can be either
single-link or dual-link or a mixture of both.=20

i.e. a two-DVI-output graphics card could have two single-link connections,
one single-link and one dual-link or two dual-link connections ... this
should be detailed either in the manual (in the specs for the card) or on
the manufacturers website ... an important thing to remember is that just
because - say - one card based around a given graphics chipset has
dual-lin=
k
connections that doesn't mean all cards based on that chipset will have -
it's up to the manufacturers whether they enable that functionality or not
on their cards.

So - to drive one of these big bitches you need a graphics card that has a
minimum of *ONE* dual link DVI connector and you need to ensure that your
connecting cable is a dual-link capable cable. There are plenty of cards
ou=
t
there that do have one or two dual-link DVI outputs and not at silly prices
- Novatech are doing a 512Mb dual-dual-link (i.e. two DVI outputs and both
dual link capable) for less than =A3120 here:

http://www.novatech.co.uk/novatech/specpage.html?NOV-79GS5
(two 30" display=
s
off one PC anyone?)

and they have a passively cooled one with 256Mb on it here:

http://www.novatech.co.uk/novatech/specpage.html?XFX-76GS
which is just ove=
r
=A370.

Phil