As Chris said, unicast is a one to one relationship and is what your computer is doing when it connects to this site. In a unicast setup, each PC musthave a unique IP address and can both recieve and transmit using it. A multicast setup is a one to many configuration. With it a PC acts as the server and only transmitts on the multicast address. Mutiple client PC's can subscribe to that same address but can only receive data on it.
As far as your display is concerned, a multicast setup allows for multiple units subscribe to the same multicast address. This allows multiple units to get their data from a single data stream. If all of the units need the same data then this saves on bandwidth. In a unicast setup, each device requires a unique IP address which means a seperate data stream would be required for each device using it. If all of the devices are working with different data then this works well but if the devices are using the same data then you are wasting a huge amount of bandwidth.
