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.