Dual Graphics Card Question

When you have 2 graphics cards in high end PCs like chillblasts etc is this to give you mulitple displays ie 4 screen running or is it to share the power demand of games allowing then to run faster so do the cards daisy chain into each other then onto one display/monitor

Thanks Nova

3 Comments

Multiple monitors

Both - I'm not sure about Ati's Crossfire system, Nvidia's SLI multiple graphics card system allow you to use up to four graphics cards together to increase 3D performance on a single monitor or to drive multiple monitors (SLI needs to be disabled for this). By using multiple graphics cards (with either ATI's crossfire or Nvidia's SLI) you can game smoothy at very high resolutions with high detail such as on 30in displays with a 2560x1600 resolution.

John

It's an either/or situation with multiple graphics cards. You can either have each card driving it's own monitors up to however many cards you can fit on your motherboard OR if the cards and motherboard all support it you can turn the crossfire/SLI function on which harnesses all the cards to work on the same processing task (i.e. rendering a game), but both SLI and crossfire currently support only two monitors.

Crossfire/SLI can be enabled/disabled in software so it's easy to switch between the two.

The cards will need to be connected together if you want to use crossfire/sli (but not for multiple monitors), this is done using special crossfire/sli connectors inside the case.

The requirements for SLI/Crossfire is that the cards support it, the monitor supports it and the game supports it, and although I've been refering to them together they're seperate things and just because one is supported by a component doesn't mean the other will be. (ATI Graphics cards support crossfire, Nvidia cards SLI, motherboards can be one or two and games are generally neither or both).

For gaming it's generally best to only consider SLI/Crossfire if you want more power than the fastest single GPU card can provide as support in games isn't universal and has a couple of potential problems like microstuttering.

EDIT: Oh, and a further proviso: Due to the initial implementation of a new display model Windows Vista will only support graphics cards using the same driver which generally means from the same brand so you can't mix ATI and Nvidia cards even if you're not using SLI/Crossfire. Windows 7 and Windows XP don't suffer from this limitation.
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