DVI/DualLink/HDMI/DisplayPort

[gte619n]

Hey guys!

I was wondering if someone could help me unravel the differences between DVI, DualLink, HDMI and DisplayPort cables and ports. I'm getting ready to build a new machine and I need a card that handles three monitors. I've been looking at a number of 1/2 height cards, but am getting a little confused by all these ports.

Do they have any large advantages/disadvantages?

My LCDs have DVI input, will these all convert seamlessly with adapters?

Are there any performance differences?

Does DualLink somehow degrade or reduce my resolution? Does Windows still recognize them a separate monitors?

thanks!

evan

 

[NoQuarter]

DVI and HDMI use the same TDMS signal and are interchangeable. You can use adapters to go back and forth between the 2 with no issues. The only difference is HDMI has an audio channel which makes it more convenient for TVs or monitors with speakers.

DualLink DVI has an extra block of pins to create a second TDMS link to the monitor increasing the available bandwidth and thus maximum resolution/refresh rate. This doesn't mean it runs two monitors. Most monitors only need/use Single Link, unless you have a pretty high resolution monitor (2560x1600).

DisplayPort is a newer format that isn't compatible with DVI/HDMI. It offers the same quality (all digital connections are going to be the same quality), but has higher bandwidth allowing for higher resolutions or hubs to drive multiple monitors off a single port.


The disadvantage to DVI/HDMI though is that each TDMS signal requires a separate clock signal provided by the GPU. Almost all video cards have only 2 such clock generators integrated into the GPU. This means regardless of the number of DVI/HDMI ports on the video card they can only output to 2 at a time. DisplayPort isn't limited by clock signal generators though. So you can hook up as many DisplayPort devices as you have connections on the back of your card, and if you don't have enough connections you can use a DisplayPort hub to make more.

So using 1 video card you can only hook up 2 DVI/HDMI monitors. If you want a 3rd monitor you either need onboard video to power one of them, a 2nd video card, or a DisplayPort capable video card and DisplayPort monitor/adapter. If you go the DisplayPort + adapter route you need an *Active* DisplayPort -> DVI adapter (Single link is fine, ~$30). Passive adapters do nothing but ask the video card to send a DVI signal out the DisplayPort port, but the video card won't have any available. Active adapters take the native DisplayPort signal and use a chip to convert the signal to DVI.

 

[gte619n]

NoQ,

Thank you so much. This is a fantastic post and really clarifies the issue for me.

As a related question, you mentioned that you could run the on-board graphics as well as a video card to get three monitors. For some reason I had thought that you could only use one or the other.

Can you run both?

 

[NoQuarter]

NoQ,

Thank you so much. This is a fantastic post and really clarifies the issue for me.

As a related question, you mentioned that you could run the on-board graphics as well as a video card to get three monitors. For some reason I had thought that you could only use one or the other.

Can you run both?

You didn't used to be able to, the onboard would automatically disable if a video card was detected. But AMD chipsets from 600 up added a 'SurroundView' option in the bios that keeps the onboard active, and Intel has a similar option on Sandy Bridge chipsets now.

So pretty much if you have an AMD system or a newer Intel system you can do it as long as you have onboard video.

 

[gte619n]

Ok great! Thanks, that certainly sounds like a very good option for my requirements. Looks like I'll be able to run three monitors out of my 2U case yet!

E

 

[MichaelD]

This is one of the most complete and thorough explanations I've ever seen on graphics cards outputs. I learned all about DisplayPort and I knew almost nothing about it beforehand. Thanks very much! :thumbsup:

DVI and HDMI use the same TDMS signal and are interchangeable. You can use adapters to go back and forth between the 2 with no issues. The only difference is HDMI has an audio channel which makes it more convenient for TVs or monitors with speakers.

DualLink DVI has an extra block of pins to create a second TDMS link to the monitor increasing the available bandwidth and thus maximum resolution/refresh rate. This doesn't mean it runs two monitors. Most monitors only need/use Single Link, unless you have a pretty high resolution monitor (2560x1600).

DisplayPort is a newer format that isn't compatible with DVI/HDMI. It offers the same quality (all digital connections are going to be the same quality), but has higher bandwidth allowing for higher resolutions or hubs to drive multiple monitors off a single port.


The disadvantage to DVI/HDMI though is that each TDMS signal requires a separate clock signal provided by the GPU. Almost all video cards have only 2 such clock generators integrated into the GPU. This means regardless of the number of DVI/HDMI ports on the video card they can only output to 2 at a time. DisplayPort isn't limited by clock signal generators though. So you can hook up as many DisplayPort devices as you have connections on the back of your card, and if you don't have enough connections you can use a DisplayPort hub to make more.

So using 1 video card you can only hook up 2 DVI/HDMI monitors. If you want a 3rd monitor you either need onboard video to power one of them, a 2nd video card, or a DisplayPort capable video card and DisplayPort monitor/adapter. If you go the DisplayPort + adapter route you need an *Active* DisplayPort -> DVI adapter (Single link is fine, ~$30). Passive adapters do nothing but ask the video card to send a DVI signal out the DisplayPort port, but the video card won't have any available. Active adapters take the native DisplayPort signal and use a chip to convert the signal to DVI.

 

[gorobei]

just for completeness:

displayport also allows you to daisychain monitors: 1 cable from card output to 1st monitor, 1 cable from 1st to 2nd, 1 cable from 2nd to 3rd, etc. though no dp1.2 monitors are available yet.

displayport can also carry audio at higher bandwidth than hdmi, as well as still having room to carry mouse and keyboard inputs back to the computer.

 

[MichaelD]

Didn't know that either. Thanks, gorobei!