How to Use 3 Monitors
I'm just migrating to a 3 monitor setup myself. Basically as long as the graphics card works, you can use it. I'm geting 2 Nvidia 8600 PCI-e cards and I'm not using SLI (Motherboard doesn't support it), however SLI is not required.
Almost all operating systems I know of support multiple monitors, as long as the gfx card is enabled, then you can use it.
As for built-in VGA ports, there's no reason that wouldn't work either, though I think most BIOSs disable the on-board display if they detect you've got a gfx card, so you may have to change the BIOS setting so that the onboard VGA is initialised.
Edit: As Will points out, Vista is a bit picky when it comes to multiple cards, all the cards need to use the same driver, so you won't be able to use onboard and another gfx card under Vista.
I would use a second computer and connect the two computers with synergy. Synergy is a software based kvm switch, so it feels like you are using one computer. It's great if like running linux, but you still need a few windows apps. You can keep the windows stuff on the computer with one monitor and have your linux box run the two other monitors. It works on mac too.
An interesting option if you can't add an additional graphics card is to use a USB video card: http://www.evga.com/products/prodlist.asp?switch=10
Assuming you're using Windows XP or Vista, you can use most any combination of video cards
My understanding of Vista is that unless you use old XP drivers, you can now only use multiple cards which share a single set of drivers.
I think this is why things like http://www.maxivista.com/ don't really work on Vista.
Related videos on Youtube
The.Anti.9 less than a minute
Right now my setup has a nice big 24" flatscreen in the center with a 19" flatscreen to the left. But I have a big gaping hole on the right.
I have a 3rd monitor to put there, but I'm not sure how to get the computer to recognize it. Do I need a graphics card with 3 ports? Can I span the monitors over non SLI-Linked graphics cards? Is it possible to plug my 3rd monitor into the on-board VGA port and have it work?
Nick Bolton almost 13 yearsAlso, there's Synergy+ (en.wikipedia.org/wiki/Synergy%2B)
dubRun over 11 yearsI was running 4 monitors using two nvidia cards. 2x22s and 2x19s That was alot of fun. I only had 1 8x PCI-E slot so I simply took a flat screwdriver to the end of the 1x PCI-E slot and put my second 8x card in that slot. Worked like a champ. Never did gaming, so can't comment on bandwidth loss using a 1x connector for an 8x card
Michael9000 over 10 yearsI dont get the reason for all the upvotes. Yeah synergy is nice, but why use one more computer, instead of a single graphicscard with 3 simultaneous outputs (ATI even has some for 6 monitors!)
Shinrai over 10 years@Michael9000 - At the time this post was written, that wasn't the case. It still wasn't the best advice then but it's terrible advice now.
Ramhound over 10 years@Michael9000 - The graphic cards that have 6 video outputs are several thousand dollars.
Eryper about 9 yearshere is the DVI one newegg.com/Product/…-pla--USB+Display+Adapters-_-N82E16812200687&gclid=CKroycO4m7YCFWunPAodnjYA9A
Ramhound about 9 years@NathanAdams - The product you found didn't exist in Jan 2012 when I made the comment. The cards that had 6 video outputs that I looked at ( when I looked ) were several thousand dollars.
Ramhound about 9 years@NathanAdams - My response was in Jan 12....