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<H2><A NAME="s10">10. Porting</A></H2>
<P> The ability of any Alpha-based machine to run Linux is really only limited
by your ability to get information on the gory details of its innards. Since
there are Linux ports for the E66, EB64+ and EB164 boards, all systems based on
the 21066, 21064/APECS or 21164/ALCOR should run Linux with little or no
modification. The major thing that is different between any of these
motherboards is the way that they route interrupts. There are three sources of
interrupts:
<P>
<UL>
<LI> on-board devices</LI>
<LI> PCI devices</LI>
<LI> ISA devices</LI>
</UL>
<P>
<P> 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.
<P>
<P> 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.
<P>
<P> Other differences between the systems include:
<P>
<UL>
<LI> how many slots they have</LI>
<LI> what on-board PCI devices they have</LI>
<LI> whether they have Flash or EPROM</LI>
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