10. Porting

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:

• on-board devices
• PCI devices
• ISA devices

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:

• how many slots they have
• what on-board PCI devices they have
• whether they have Flash or EPROM