The wheel spins to place the correct letter under the hammer. Once were popular because they produced a very high quality output. But drops of ink is sprayed on the paper. Lower quality, cheaper. Similar to wax transfer, but uses color dyes.
Dyes merge to create the color instead of being layered on top of one another.
Cylinder spins and slams against the paper when the proper character is in the right position. One revolution of the cylinder can print an entire line. So, if application program thinks its talking to a printer, it can assume the type of data to send out the interface. Interfaces Serial - characters sent one bit at a time over a single wire. Network Interface - a board or device that understands network protocols and collects the characters from the network wire.