Portability comparison (2/3)

"Glue layer" approach (NT HAL, NetBSD)
Single abstraction used by most drivers
Small amount of code to write for new platform
Small learning curve
Time to port the OS is much shorter
Bugs that occur rarely on one platform are often found quickly on other platforms, resulting in more robust code everywhere

NetBSD currently supports 12 CPU families and 32 system families from a single source tree