Greenville has cable television subscription available. Cable television is a system of providing television programs to consumers via radio frequency (RF) signals. These signals are transmitted to televisions through coaxial cables or optical fibres. The signal transmitted may be either analog or digital. Most current television sets come equipped with a cable tv tuner that enables them to receives analog cable signal. For household use in Greenville, a set top box would be needed to receive digital signals. These boxes can be of two types- SD and HD set-top boxes, which come equipped with smart cards. Cable TV subscription can be of various kinds in Greenville, such as basic (transmitted without any television encryption or other scrambling methods), which are free-to-air. Their main earnings are via advertisements. Premium cable includes networks that scramble or encrypt their signals so that only upon payment of additional monthly fees can one legally view the channels (the signals are unscrambled by an installed cable converter). Recently, there has been a move towards allowing consumers to pick and choose individual channels for a personalized bonquet. This is called A la carte cable television, and this is not entirely implemented yet. Cable tv subscriptions are popular, with more than half the American homes having a basic cable television service installed.