If you want more performance so you can play the latest games at high resolutions and maximum quality, you need a decent graphics card. But how do you know if your new card will fit inside your PC's case and how do you know if it is compatible with your existing set up.
Many PCs rely on so-called 'integrated graphics' which is either a chip on the motherboard or one built into the CPU itself. Other PCs have a 'dedicated graphics card', which plugs into an expansion slot on your PC's motherboard.
You can usually tell which type your PC uses by the location of the Graphics connector port you use to plug in your monitor. If it is located in among the other ports, such as USB and Ethernet, then it's 'integrated graphics'. If the port is separate to the others, and there's more than one port, such as a pair of DVI outputs, HDMI or DisplayPort, it's likely to be a 'dedicated graphics card'.
To fit a 'dedicated graphics card' you'll need both a PCI Express expansion slot and a corresponding slot in the PC's case, with a removable back plate where the connections will sit.
On many PCs, there will be a few expansion slots on the motherboard. Typically they will all be PCI Express, but for a graphics card you need a PCI Express x16 slot. There are three versions of this slot, but they are all backwards compatible, so a modern PCI Express 3.0 graphics card will work in a motherboard with a PCI Express x16 2.0 slot.
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If your motherboard has two PCI Express x16 slots it's most common to use the upper-most one for a graphics card, but if you're fitting two cards in an NVidia SLI or AMD Crossfire setup, you'll need both. Check which standard your motherboard supports before investing in a pair of cards, though.
More powerful graphics cards tend to have large fans to keep them cool, and this makes them twice as thick as a 'single-height' card. The way most PCs are built means that the fan assembly will often be underneath the card rather than on top of it, so you will need an unused slot - and back plate - directly underneath the PCI Express x16 slot.
Plus, you need to measure the distance from the back plate to any components which would block a long graphics card at the front of your case. Don't forget that some cards have their power sockets on their back edge rather than the side, so you'll need to add about 30-40mm to the length of your chosen card to guarantee it will fit. If you're unsure how long a card is, ask the manufacturer, seller or try pc forums to find someone who owns that card already and can confirm how big it is.
Even if you have PCI Express x16 slot and plenty of room, you'll need extra power for most graphics cards. Your Power Supply Unit (PSU) is likely to have PCI-E power connectors, but they may be bundled up and tied out of the way if no graphics card is currently fitted. These connectors are usually black, marked as PCI-E and have six pins in a 3x2 arrangement. If your PSU doesn't have these, you can buy adaptors which connect to the standard four-pin power or SATA connectors.
Be careful with graphics cards that require two PCI Express power connectors as each of these should be connected to a different 12v rail of the power supply. On most PSUs this means connecting each of the two adaptors to a different 'daisy chain' of power connectors, and not to the same chain.
Finally, make sure your PSU has enough power above what the existing components are drawing to power your new graphics card.
It can be tricky to work out if yours does, but a good rule of thumb is that high-end graphics cards will require at least a 600W PSU, if not more. It's wrong to assume that a PSU can output its maximum power rating continuously, and you're sure to run into problems if your components are drawing more than around 80 percent of the PSU's top rating. Again, it's fairly easy to check how much power a graphics card draws from its specifications by searching online.