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Interrupt Lines
The interrupt request line serves as the "pull line" for the
expansion cards to get attention of the CPU. The interrupt request line
(IRQ) works like the string you pull on a bus when you want the bus to
stop. On a computer, there is a limited amount of IRQ lines available.
Although, on most computers the amount provided is sufficient. Without
an IRQ, some devices will not even operate properly.
Note: If at all possible, avoid configuring IRQs for devices.
It is one of the least enjoyable aspects of the computer.
DMA Channels
Similar to IRQs, DMA channels are assigned to each individual hardware
device. DMA channels allow the hardware device to bypass the processor
and write directly into main memory.
I/O Addresses
I/O addresses are also commonly known as I/O ports or hardware ports.
When the CPU wants to send instructions to the expansion cards it uses
the I/O addresses. The I/O addresses "deliver the message" to the device,
and then, the device responds appropriately through the data bus or DMA.
Clock Signals
The clock signal used by expansion cards is the same as the one we
discussed earlier, in the CPU section. If you would like to review this
information again, please do so in the CPU section.
Bus Mastering
Bus mastering allows expansion cards to communicate directly with
other devices without having to go through the CPU. Bus mastering allows
the expansion cards to read or write directly from another device. For
example, if one of your cards needs to store some information on the hard
drive, it doesn't have to request the CPU to perform the operation. Bus
mastering introduces a large increase in performance for expansion cards.
Therefore, the more bus mastering devices, the faster the bus is capable
of operating.
Now that you are familiar with the concepts involved with expansion
slots, lets discuss the various types of expansion slots available. Please
continue the tutorial with Expansion Slot Types.
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