A+ Hardware Service Technician: Computer Hardware, System Boards, and Storage Devices

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Expansion Bus

Expansion Bus Speed

The different types of expansion busses operate at different speeds. The speed is controlled by a bus clock. The speed is controlled so that the motherboard/CPU only has to receive and transfer the amount of data it can handle or process at a given time. For example, a slow processor may not be able to handle the amount of data a very fast bus could transfer, so the data transfer speed is regulated to ensure the data does not overload the processor.

Interrupts

Interrupts are commands from a device to signify to the computer to stop. Basically, the operating system will continue running software code until the code is complete or until it receives an interrupt request. In hardware, the interrupt request (e.g. IRQ) has a value associated with it for each particular device.

DMA Channels

DMA Channels, or Direct Memory Access Channels, were designed to allow certain devices direct access to the memory. In the original PC, the system was designed so the CPU would control all access and act as the “traffic cop.” DMA was designed to allow certain expansion cards or devices to bypass the “middle man” and access memory directly. DMA was only used in ISA and its cousins EISA and VLB. PCI expansion cards do not use DMA.

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