Every effort is made to keep everything cleanly split into 'MachineDependent' (MD) and 'Machine Independent' (MI) areas. For example,an Ethernet chipset would have a single MI core hardware driver,which would be matched with appropriate MD bus attachment code for agiven platform. Not all drivers are as clean as we would like forhistorical reasons, but any new driver will be, and old driversare in the process of being converted across.

As a concrete example, a driver, such as thefxp(4) Intel i82557,i82558, and i82559 Ethernet interface driver, would be used to operatean Intel EtherExpress card in analpha,arc,cats,cobalt,i386,macppc,or aprep system, all of which have pci slots.

Additionally, the same driver would operate a Cardbus device which usedthe same chipset. This means that the code is written once, and usedmany times in many places. If mistakes had been made in the originalimplementation of the driver, use on such a wide variety of systemswould usually bring problems to the surface more quickly. Understandingwhat makes a PPC different from an i386 leads to well thought outdesign, and better code.

NetBSD's slogan is"Of course it runs NetBSD", and with good cause. At the time of writing NetBSD providesformal releases for 53architectures, and has integrated ports for fourothers. Those numbers can be deceptive - within one platform(mac68k), there are 93 differentmachines, of which 89 are currently supported (37 fully).