The video card is the component in your computer that translates the video signal from your computer to your monitor. Without one you can't see what is going on with your computer and therefore can't really do anything with it. Many computers have video cards built into the motherboard and others have add-on cards that are plugged into a certain type of video slot on the motherboard.
Just because your computer uses a built in video card on the motherboard doesn't mean you can't upgrade and add a standalone card. Just make sure you get the right type to match the type of slot you have available on your motherboard.
When it comes to choosing the right video (graphics) card, you need to determine what you will be doing with your computer. Will you be surfing the internet and writing letters? Playing high end 3D video games or maybe editing photos and home movies?
You have 3 choices when it comes to video cards. AGP (Accelerated Graphics Port), PCI (Peripheral Component Interconnect) and PCI Express. Each one has a different level of performance.
PCI is the oldest of the three types of video cards. PCI is also used for devices such as sound and network cards. PCI uses a shared bus topology to allow for communication among the different devices on the bus. It provides for a bandwidth of up to 133 Mbps with a 64 bit version supporting up to 512 Mbps. PCI video cards can still offer high performance when you get a card with a lot of on board memory (128+ MB). This is your best and cheapest bet for the home or business user who is going to do general purpose computing.
AGP was designed for use with 3D graphics applications. AGP uses a dedicated point-to-point channel so that the graphics controller can directly access main memory. It provides for a bandwidth of 266 Mbps to 1.07 Gbps. To use an AGP video card your motherboard must support it and include an AGP slot for the card unless its built into the motherboard itself. Most modern computers will support this type of card yet now they are being replaced with PCI-Express slots on new computers.
PCI Express expands on and doubles the data transfer rates of the standard PCI interface. PCI Express is a two way (point to point bus) serial connection which avoids performance problems that can arise from bandwidth sharing on a common bus. Regular PCI uses a single parallel connection. It provides greater tranfer speeds than PCI or AGP . It is also used with other devices such as network cards to achieve greater throughput than standard PCI. PCI Express is also compatible with existing PCI systems. It is the replacement for AGP for the latest generation of video cards.
There are several types of PCI Express video cards including:
PCI Express 1x 250  MB/s
PCI Express 2x 500  MB/s
PCI Express 4x 1000  MB/s
PCI Express 8x 2000  MB/s
PCI Express 16x 4000  MB/s
PCI Express 32x 8000  MB/s