lpd printing system

lpd is line printing daemon. unix 1st printing system. Initial printing involved just dumping the text file to the printer connected via the parallel port. lpr is the program which submitted the job to the spooling daemon. But lpr did not support any of the options supported by the device except for usual options such as duplex and number of copies. Why do we need a spooling daemon? So that the printing interface can be separated from the the application world. Instead of each application supporting its printing, now they can communicate with a centralized printing system which takes of all the printing in the system. The application just need to handover the print job to this system and go back to doing what they were doing. The spooler will keep the print jobs together from all the applications and send them as an when the printer is available. This is the common concept of printing in all the OS's.