Control systems are, nowadays, implemented by means of computers or DSPs.

The use of processors in the loop has several advantages and some disadvantages.

Controllers are easily implementable, and can be tuned on-line.

Controllers are small (and cheap).

Complex controllers (i.e. controllers performing several operations) can be easily implemented.

Controller design can make use of symbolic SW tools.

Processors can be used to implement monitoring and safety tasks.

The closed-loop system contains continuous-time components and discrete-time components (and interfacing devices): it is a hybrid system.

The analysis of the closed-loop system is often based on approximations.

Digital controllers are very sensible to numerical errors.

Controller design is more involved and (often) non-intuitive.

The notion of frequency for discrete-time systems is non-intuitive.