4 Porting

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The major thing that is different between any of the motherboards mentioned above is the way that they route interrupts. There are three sources of interrupts:

All the systems use an Intel System I/O bridge (SIO) to act as a bridge between PCI and ISA (the main I/O bus is PCI, the ISA bus is a secondary bus used to support slow-speed and 'legacy' I/O devices). The SIO contains the traditional pair of daisy-chained 8259s.

Some systems (e.g., the Noname) route all of their interrupts through the SIO and thence to the CPU. Some systems have a separate interrupt controller and route all PCI interrupts plus the SIO interrupt (8259 output) through that, and all ISA interrupts through the SIO.

Other differences between the systems include:

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