The advantage of HDMI for dual displays

February 6, 2012

One of the interesting things that happened during my five years of hardware hibernation is that when I woke up, even low end (aka passively cooled) graphics cards could suddenly drive two digital outputs. Back in 2006 it was common for cards to have one analog and one digital out (eg, the ATI X300 in my work machine had VGA plus DVI), but getting dual digital out required an expensive card with an often noisy fan.

(I actually went through two such cards at work, each time deciding that I couldn't see enough advantage to driving my second display digitally instead of via analog VGA to be worth putting up with the noise. Possibly I wasn't sensitized enough to VGA artifacts and issues.)

What I have to thank for this is HDMI. Now, I'm aware that there's a lot to dislike about HDMI (see eg HDCP), but from my perspective the great thing about it is that it's given even low end cards a second digital output; it seems to be common for cards to have both DVI and HDMI. Some modern displays can be directly driven over HDMI and for the others, a simple cable will go from HDMI to DVI. And so my 2011 low end, passively cooled graphics card will now drive both my displays at work digitally, one directly with DVI and one with an HDMI to DVI cable, which is something that I never managed nicely before now.

(I believe that this has resolution limits. I don't use really big LCDs, so these haven't affected me.)

One of the interesting questions for me is why this happened. Why did graphics card vendors start putting HDMI on everything, where they only rarely did dual DVI? I think that part of the reason is that HDMI uses a physically small connector. DVI uses a relatively big connector and if you look at the back of a graphics card (especially a dual-DVI graphics card), there just isn't all that much physical space there; it's hard to get two DVI connectors and anything else in. By contrast, HDMI connectors are much smaller (I can't find the exact dimensions, but some sources say a third of the size). This makes it much easier to find the physical room for a HDMI connector on a card edge and on a circuit board.

(For example, my current graphics card just fits in VGA, DVI, and HDMI connectors with basically no spare room.)

PS: I don't think it's a coincidence that DisplayPort, the theoretical next generation replacement for DVI, also has a small connector. I suspect that the graphics card layout designers had a few words with people.

(Of course pretty much everything seems to be going to small connectors, with large ones proving awkward. Consider SATA versus IDE, for example. Someone who knew more about electronics than I do could probably write a fascinating article about all of the developments that made narrow-connector interfaces feasible and preferable to the old wide connector ones.)


Comments on this page:

From 24.126.141.58 at 2012-02-07 10:12:53:

The main differences for most of the small connectors is the switch from parallel to serial. That's the main difference between PATA and SATA, and PCI express vs the old PCI. For the remaining parallel connectors, like HDMI, DP, etc..., the driving force is the need on small laptops and cell phones, and since everyone wants standard cables, all other devices get that too. It helps immensely that most of the new standards are backwards compatible with at least DVI.

By cks at 2012-02-07 10:42:00:

The parallel to serial switch is the obvious factor in the size shrink. What I'm wondering about is electronics developments that made serial protocols of this nature feasible and even preferable to earlier parallel protocols.

(I suspect that part of the downsizing was better fine manufacturing machinery so that the physical wires and wire connectors could shrink, but I don't know for sure.)

Written on 06 February 2012.
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