Motherboard Expansion Interfaces
The history of the PC has seen many different types of expansion slots. Some, like the MCA (Micro-Channel Architecture) interface, and the Video Electronics Standards Association's VESA interface, never really caught on and have quietly faded into history. A few newer interfaces, such as the ACR and the PCI-Express interfaces, are just now beginning to achieve acceptance.
The diagram on the right is a bit dated, but it should still give you a pretty good idea of what the major components of a motherboard are. (There's a diagram of a newer mobo toward the bottom of this page.) Of course, every motherboard is different, but for the most part they all contain the same kinds of components. Please click the image and spend a few minutes studying it. Your motherboard's manual will have a diagram help you find the components on your particular mobo.
Recognizing Expansion Slots
Being able to recognize expansion slots and understand their uses is critical to designing and building your homebuilt computer.
The three most common expansion interfaces in current use are:
PCI (Peripheral Component Interconnect). The PCI interface is used for all kinds of expansion cards and is the most common expansion interface. All sorts of PCI expansion cards are available, including modems, add-on hard drive and I/O controllers, network cards, sound cards, some older video cards, and all manner of specialized controllers for industrial machinery.
AGP (Accelerated Graphic Port). The AGP interface is used only for video cards. It represents a significant improvement over older PCI video cards. But even within AGP, the standard has been improved and data transfer rates have increased. When selecting an AGP video card, one factor to consider is whether your motherboard is able to support it properly. For example, you shouldn't purchase a 4X AGP video card for a motherboard that only supports 2X AGP, nor vice-versa.
PCI Express. The PCI-E interface theoretically can be used for almost any kind of I/O device, but is most popular as an interface for high-end video cards because of its massive data transfer capabilities (more than 250 Mb/sec, as of this writing).
Here's a diagram of a more modern motherboard, the Gigabyte GA-M61VME-S2, side-by-side with the accompanying diagram from the motherboard manual. (Click to enlarge it.)
The bottom line is, when choosing a motherboard for your homebuilt computer, be sure that it has enough of the correct types of slots to accommodate the expansion cards you wish to install.