Thread: Motherboards I/ O Bus Slots

All motherboards have one or more system I/O buses that are used to expand the computer's capabilities. These buses work closely with expansion cards. The slots in the back of the machine are where expansion cards are placed. These slots allow you to expand the capabilities of your machine in many different ways, and the proliferation of both general purpose and very specific expansion cards is part of the success story of the PC platform. Most modern PCs have two different types of bus slots. The first is the standard ISA (Industry Standard Architecture) slot; most PCs have3or40f these. These slots have two connected sections and start about a half-inch from the back of the motherboard, extending to around its middle. This is the oldest bus type and is used for cards that don't require a lot of speed: for example, sound cards and modems. Older systems may have ISA slots with only a single connector piece on each; these are 8-bit ISA slots and will only support 8-bit ISA cards.

Pentium systems and newer motherboards also have PCI (Peripheral Component Interconnect) bus slots, again, usually 3 or 4. PCI is much faster and shorter than ISA. PCI is a high-speed bus used for devices like video cards, hard disk controllers, and high-speed network cards. The newest PCs add another new connector to the motherboard: an Accelerated Graphics Port slot (AGP). AGP is not really a bus, but is a single-device port used for high-performance graphics. Older systems use VESA Local Bus, or VLBslo15 instead of PCI to connect high speed devices. This is an older bus which began to be abandoned in favor of pel at the time the Pentium was introduced. VLB Ilots look like ISA slots, only they add third and fourth sections beyond the first two. This makes their connectors very long, and for that reason VLB cards are notoriously difficult to insert into or remove from me motherboard.



Some motherboards incorporate a so-called "shared" ISA and PCI slot. This name implies a single Ilot that can take either type of card, but that isn't possible because the two slot types are physically mcompatible. In order to save space while maximizing me number of expansion slots, some designers put an ISA slot on the board right next to a PCI slot; y011 men have the choice to use either the ISA or the PCI slot, but not both. This design is possible because ISA cards mount on the left-hand side of a slot position, while PCI slots mount on the right-hand side.