Today most of digital logic is based on ready made IC form. IC 's are microminature complete logical circuits contained in a single package. Their design is such that they can be interconnected to from complete systems without being necessity of an in between discrete component.
The TTL integrated circuit has become very popular.TTL integrated circuit operates on +5V supply.Tolerance in supply voltage is 5%.TTL is a positive logic system.It means binary zero=zero volts and binary one=5 volts.