Installing an additional video card

For 3 or more monitors you'll probably need to install an additional video card. There are also some 4- and 8-monitor cards, but those are quite expensive and mostly geared towards business applications, usually the better solution is to get multiple dual cards.

To determine what type of video card to get, first check what free slots your system has. Here's a picture of a system with 4 PCI Express slots and 2 regular PCI slots:

Most PCI Express video cards are x16, which means they need an x16 slot. On the system pictured above, all slots have x16 length, meaning you can also install an x16 card in one of the x8 slots, but it might not run at full speed (usually this won't be a problem). If your system only has a single x16 length slot, you could get an x1 video card, most manufacturers offer those under their line of professional video cards. An x1 video card will fit into any PCI Express slot.

PCI Express x16 video card

PCI Express x1 video card

If your system doesn't support PCI Express, you'll have a single AGP slot for video cards, and one or more regular PCI slots. This means that your first video card will be an AGP card, and any additional video cards need to be PCI.

The video cards don't need to be identical (brand, model or chipset), but if you're purchasing new video cards I would recommend getting identical cards, this way you only need to install a single video card driver, and you should have no compatibility issues. The only exception is Windows Vista, it requires that each video card use the same driver, which means you'll need video cards with at least the same brand of chipset, for example ATI or Nvidia.

With multiple video cards installed, the BIOS screen shown during startup will only be shown on a single video card. To change which card gets used for the BIOS, enter BIOS setup and look for an option which lets you change the primary video card:

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