A laser printer comprises a printer body, a developing device disposed in an inside of the printer body with a photoconductive drum for converting a latent image formed on the outer surface of the photo conductive drum to a toner image, a laser scanning unit projecting a laser beam to the photoconductive drum to form an electrostatic latent image thereon, a paper feeding unit for feeding paper into a printing unit, and a toner supply unit supplying toner to develop the electrostatic latent image formed on the photoconductive drum. The toner supply unit is removably disposed at a printer body of the laser printer. The developing unit develops the electrostatic latent image on the photoreceptor drum into a visible image with a supply of toner thereon and then forming, with the supply of a transfer voltage between a transfer roller and the photoreceptor drum. The developing unit houses a photo conductive drum, a charging roller that uniformly charges the outer surface of the photo conductive drum rotating, a developing roller for converting a latent image, and a toner supply roller, and a toner housing. The toner cartridge is disposed at the printer body as being connected to the housing through a preselected toner supply passage. When the toner is exhausted, the developing unit must be replaced with new one.

Laser printers print images by drawing an electrostatic image on a photosensitive drum with laser beams and depositing a toner on a portion charged with a static electricity. A laser printer receives data outputted from a personal computer and outputs the received data as an image. The laser printer generates an image on a piece of paper by scanning a focused laser beam over a cylindrical photosensitive drum. The radiation from a laser is shaped, and imaged onto a film plane to produce a desired spot size. The spot, called a pixel, forms the smallest element of the image. The laser spot is scanned in the line direction, and the media is moved in the page direction to create a two dimensional image. In order to draw the image with this laser beam, a light source device using a laser diode is employed. The light source or laser beam is irradiated to a rotating polygon mirror so as to scan a recording face formed on a hologram disk. The resolution of the image is determined by the number of scan lines per inch (lpi) and the density of pixel values along each scan line, as measured in dots per inch (dpi). A typical high-resolution laser printer has 600 scan lines per inch and 600 dots per inch along each scan line. In a laser printer, print data such as document data or image data are received from external equipment such as a host computer to develop the print data into printable bit image data. The laser printer performs accurate operations and communicates with a computer.

Laser printers use a focused light beam to expose discrete portions of an image transfer drum so that these portions attract printing toner. Toner is a mixture of pigment (typically carbon black) and plastic. Monochrome laser printers use a single laser scanning unit (LSU) and a single organic photoconductive cell (OPC) drum. Color laser printers employ four printing stations, one each for black, magenta, cyan and yellow toners, and thus four LSUs and four OPCs photosensitive drums which correspond to the respective four colors are used. Laser printers generally utilize replaceable toner cartridges which often include a variety of sensors that interact with the laser printer in order to indicate the status of the cartridge such as toner level, print quality and general cartridge function. A large number of types and sizes of toner cartridges are currently available. Each toner cartridge is provided with its own specifications such as operating perimeters and toner fill limitations.