Running two monitors from DVI

Only if you're lucky.

The PC queries the screen on a DVI port to read the EDID information (supported resolutions, colour depths and refresh rates etc) if both screens are plugged in the PC will "hear" scrambled replies.

If you unplugged one screen while the PC booted, then plugged the other in, provided the 2nd screen supported the resolution the PC had chosen to use with the 1st screen, it might work, but I doubt the TMDS links really expect to be split in such a way, and being terminated twice could set up reflections of the signal, but if it happens to work without too many sparklies ...

Have you checked that you don't have two outputs on the graphics card? Even the cheap £20 ones usually do.

In my complete ignorance of these matters I thought all computers would let you plug in two monitors.

Bill

BIG - and incorrect - assumption.

I've never seen a cheap graphic card that sports a DVI output that doesn't also have a VGA connection also.

That's nice for you. I've never pissed around with cheap graphics cards, so I have no reason to doubt you. I've seen plenty of dual-output PCs, too.

Equally, you have no reason to doubt me when I say that I have seen and worked with plenty of PCs where the onboard graphics are DVI only, and I've seen and worked with plenty of upgrade graphics cards that are DVI only. Sometimes you get an adapter dongle, but not always.

I'm not doubting you, but as I said, I've never seen one without at least a VGA as well and I've seen and fixed/built many a computer.

The last three PCs I built used pretty bog standard Intel motherboards, and to get the (other) specs I wanted I had to get boards with no VGA (just DVI and DisplayPort). In two cases I had to buy cheap VGA cards so that I could use the existing KVMs.

Understood, but in my experience, most have at least 2 outputs for using dual monitors.

Adrian! Just found this snippet from a PC link, which supports my claim that most cards will run dual monitors:

"Maina Njuguna asked me what's required for a new desktop to run two monitors."

"First, you need two monitors. You'll also need a graphics card that supports two monitors. It's a pretty standard feature, these days. In fact, you'd probably have a hard time finding a new graphics card that doesn't. Even graphics integrated into a new motherboard will likely offer this support. You can easily check the back of your PC to see how many monitor connectors it has."

But it is from PCWorld.

I know I use a number of machines where number of active monitors supported is less than number of available connections (one example is laptops with HDMI and VGA that do not allow 3 screens). I think Dual screen support is more more common than it used to be though.

Indeed and if they don't support using 2 connections, quite often a cheap splitter adaptor will suffice, assuming that the system will support it.

As for the article from PC World, many other sites agree with PC World's statement. Even my 4 year old laptop runs 2 monitors using 1 HDMI and 1 VGA cons.

In message , at 09:15:30 on Wed, 8 Jan

Of the eight computers I can see from where I'm sat, only one of them does. And none of them have HDMI.

It is here - complicated by the fact its an Acorn computer. I have an aftermarket video card for it which does DVI - and allows much higher resolution etc than the base machine's approx SVGA. The results are super. And it's a CAD prog I use most on that machine - the results of which I want to display on the TV. At the moment I do use VGA for that - but it's not ideal. An MDF which suits the TV doesn't suit the monitor.

Aren't most dual outputs designed for two monitors showing different things? And are you absolutely sure a VGA and DVI can be used at the same time to feed two monitors?

There's nothing new about running two or more monitors. Macs you could buy in 1987 could do it. For the last five years or so before I retired in 2008, I was running a MacPro with three dual-port video cards, to which five displays were attached. I used two for development and three for network monitoring.