Tim wrote:
I'm going to be adding an outboard graphics card to my PC. It has, one
each, a DVI-D, a displayport, and and HDMI port. My two monitors both have
DVI-D ports. I know I will need to get an adapter cable of some sort to
connect the second DVI-D monitor to either one of the other ports. Which
one would be best the displayport or the HDMI?
FYI, my second monitor also has a VGA port that is currently how it is
driven.

You didn't tell us the native resolution of the monitors.

DVI-D ------------------- DVI-D monitor (dual link for 2560x1600 ???)
(single link for 1920x1200 ???)

DisplayPort --+--- active_adapter --- VGA $20 (uses +5V on DP cable)
|
+--- passive_adapter --- single Link DVI-D
|
+--- passive_adapter --- HDMI

HDMI ---------+--- active_adapter --- VGA
|
+--- passive_adapter --- single Link DVI-D

Active_adapter have a chip inside the cable assembly or
lengthened connector, that "converts" formats. The cable
has +5V power for low power items, and that's how the
chip is powered. There have been some adaptation devices
in the past that use a USB cable for additional +5V.

Passive_adapter rely on the probing of the monitor to
uncover what adapter scheme is being used. Passive is "just wires".
No power is used. Passive is generally used between
a digital_source and a digital_destination.

There might be some active_adapter devices for making
dual link DVI-D, which would give sufficient resolution
to drive an Apple 30" Cinema display 2560x1600 DVI-D or so.
That would be a case of "digital adaptation" at high
speed, and a "remapping" to make the two necessary link signal sets.
If the dongle needs a memory chip and has a one or two
frame time "thru_delay", the dongle will be marginally
more expensive. (They can't always economically fit the
RAM for a frame buffer, inside a dongle adapter, so it's
a two chip solution.)

If you're playing first person shooter games, you likely
wouldn't do what is in the previous paragraph (too much
thru_delay).

The Wikipedia article for DVI will explain the resolution
limits on single link DVI versus dual link DVI.

*******

At low resolutions, you can't see the difference between
VGA and one of the digital methods. As the resolution
rises, there are reflections and ringing on the VGA coax
wires which make the digital cabled version of the image
look like the better option. Digital doesn't degrade in
exactly the same way as analog VGA.

On the video card I purchased at the end of last year, I use this.

DisplayPort --+--- active_adapter --- VGA $20 (uses +5V on DP cable)

The resolution is 1440x900 on a cheap monitor, and it
looks fine. None of my monitors have a wealth of
connectors on them, so you take what you can get here.

And this is the year to stock up on adapters. Don't
wait five years to go shopping for a second one, as
eventually they'll disappear from the market. We're
at "peak flux" in terms of the adapter mess at the moment.

Paul