A printer that uses a laser to write charges onto a drum which then is dusted with toner to produce an image copy which is pressed against the paper to transfer that image to the paper. The paper is then heated and pressed to bond the toner to the paper and produce the output. The technology of a laser printer is quite similar to that within an electrostatic copy machine (Xerox machine).

In producing output the first thing a laser printer does is to assemble the image of the page to be printed in the printer's memory. Approximately 1MB of memory is generally used for most home laser printers; higher amounts of memory would be used for higher resolution machines.

Once the image is constructed, the bits in memory must be transferred to a rotating electrostatic drum which then picks up toner on areas that need to be black on the paper. There are two different types of engines in a laser printer:

• Write black. In the write black engine the drum is given a positive charge in areas where toner must be in order to produce a black image on the paper.
• Write white. In the write white engine the drum is given a negative charge in areas where there should be white space on the paper output.

Toner is attracted to the positively charged areas of the drum and repelled from negatively charged areas. Once the toner is on the drum the paper and drum are placed into contact and an electrically charged wire behind the paper pulls the toner off of the drum and onto the paper. The paper is then fed through heated rollers which both press and fuse the toner to the paper. The drum, in the meantime, continues to rotate past another charged wire which cleans any residual toner from the drum and gives it a uniform charge so it can be used in another pass. One sheet of paper generally prints with two to three rotations of the drum which is why, if there is a defect on the drum, you might see a regular pattern of spots on your output; two or three to a page.

In the first laser printers a laser beam was used to scan across the drum to create the charged areas. Later versions also use a row of light emitting diodes (LEDs) and/or liquid crystal shutters in front of a light to create the charged area images on the drum.