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A Mach *task* is a collection of resources, a [[virtual_address_space]], and a
[[port name space|port]].  They depend on [[thread]]s for executing program
code: a task alone has no means to do so.

Switching from one task to another one involves doing a *context switch*, which
is usually not a cheap operation, as it involves switching the hardware's idea
of the memory layout ([[virtual_address_space]]), amongst others.

Mach tasks are distinct from [[UNIX processes|unix/process]] in that they
provide less facilities.  In processes, there are [[unix/signal]]s, process /
group / session IDs, [[unix/file_descriptor]]s and many other things.  Tasks
are used for resource allocation and sharing; they are *resource container*s.