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Expansion Slots

If a computer is to be useful, the CPU must communicate with the outside world, including other motherboard components and adapters plugged into the motherboard. An expansion slot is used to add an adapter to the motherboard. It has rules that control how many bits can be transferred at a time to the adapter, what signals are sent over the adapter’s gold connectors, and how the adapter is configured. Figure 3.26 shows expansion slots on a motherboard.

Figure 3.26

Figure 3.26 Motherboard expansion slots

Expansion slots used in PCs are usually some form of PCI (Peripheral Component Interconnect), AGP (Accelerated Graphics Port), or PCIe (PCI Express). Other types of expansion slots that have been included with older PCs are ISA (Industry Standard Architecture), EISA (Extended Industry Standard Architecture), MCA (Micro Channel Architecture), and VL-bus (sometimes called VESA [video electronics standards association] bus). A technician must be able to distinguish among adapters and expansion slots and be able to identify the adapters/devices that use an expansion slot. A technician must also realize the abilities and limitations of each type of expansion slot when installing upgrades, replacing parts, and making recommendations.

An alternative to an adapter plugging directly into the motherboard is the use of a riser board. A riser board plugs into the motherboard and has its own expansion slots. Adapters can plug into these expansion slots instead of directly into the motherboard. Riser boards are used with rack-mounted servers and low-profile desktop computer models. The riser card is commonly inserted into a motherboard slot or attached using screws. Figure 3.27 shows how a riser board attaches to a motherboard.

Figure 3.27

Figure 3.27 Installing a riser board

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