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diff --git a/book/en/src/by-example/software_tasks.md b/book/en/src/by-example/software_tasks.md
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@@ -1,9 +1,20 @@
 # Software tasks & spawn
 
+Software tasks, as hardware tasks, are run as interrupt handlers where all software tasks at the
+same priority shares a "free" interrupt handler to run from, called a dispatcher. These free
+interrupts are interrupt vectors not used by hardware tasks.
+
 To declare tasks in the framework the `#[task]` attribute is used on a function.
 By default these tasks are referred to as software tasks as they do not have a direct coupling to
 an interrupt handler. Software tasks can be spawned (started) using the `task_name::spawn()` static
 method which will directly run the task given that there are no higher priority tasks running.
+
+To indicate to the framework which interrupts are free for use to dispatch software tasks with the
+`#[app]` attribute has a `dispatchers = [FreeInterrupt1, FreeInterrupt2, ...]` argument. You need
+to provide as many dispatchers as there are priority levels used by software tasks, as an
+dispatcher is assigned per interrupt level. The framework will also give a compile error if there
+are not enough dispatchers provided.
+
 This is exemplified in the following:
 
 ``` rust