Task-base is new way of creating basic root filesystems. Instead of having each machine setting a ton of duplicate variables, this allow a machine to specify its features and task-base builds it a customised package based on what the machine needs along with what the distro supports.

To illustrate, the distro config file can say:

DISTRO_FEATURES = "nfs smbfs ipsec wifi ppp alsa bluetooth ext2 irda pcmcia usbgadget usbhost"

and the machine config:

MACHINE_FEATURES = "kernel26 apm alsa pcmcia bluetooth irda usbgadget"

and the resulting task-base would support pcmcia but not usbhost.

Task-base details exactly which options are either machine or distro settings (or need to be in both). Machine options are meant to reflect capabilities of the machine, distro options list things distribution maintainers might want to add or remove from their distros images.