The printing system in accordance with the present invention includes a computer with a print setup program displaying a print command window on a monitor screen and at least one printer, each with two or more paper source cassettes, connected to the computer, wherein the print setup program detects all the printers connected to the computer and all the paper source cassettes provided to each printer and provides a number of print command execution buttons corresponding to the detected cassettes in the print command window, to let a user to select any button among the print command execution buttons, so that a user can print out from a desired cassette.