As a model increases in size and complexity, you can simplify it by grouping blocks into subsystems. A subsystem is a set of blocks that you group into a single Subsystem block.

Using subsystems:

When you make a copy of a subsystem, that copy is independent of the source subsystem. To reuse the contents of a subsystem across a model or across models, use a library or convert the subsystem to a referenced model. To identify the most suitable model component for your application, see Component-Based Modeling Guidelines.

A subsystem can be virtual or nonvirtual. A virtual subsystem provides graphical hierarchy in a model and does not impact the execution of a model. A nonvirtual subsystem executes as a single unit within a model. For information on conditionally executed subsystems, see Conditionally Executed Subsystems and Models.