Output Devices Output Devices An Output device is

Output Devices

Output Devices • An Output device is any device which will show the information processed by the CPU. • Output devices translate signals from the CPU into a human readable form or into a form suitable for reprocessing by the computer at a later stage. • Example of output devices include the speakers and the printer.

Laser Printers

Laser Printers • A laser printer is a common type of computer printer that rapidly produces high quality text and graphics on plain paper. • Laser Printers are used in many workplaces because they are quiet, they print a large number of sheets very quickly and they produce high quality documents.

How it works • Laser Printers are also called thermal printers, because they print using heat. • Laser printers do not use ink to print. • Laser printers use a type of dry, powdered, electrically charged ink called toner. The printer places the toner on an electrically charged rotating drum and then deposits the toner on paper as the paper moves through the system at the same speed the drum is turning. This involves a complicated process of optical, electrical, and mechanical systems.

The process of printing is broken down into 7 phases: 1. Raster image processing 2. Charging 3. Writing 4. Developing 5. Transfer 6. Fusing 7. Cleaning

• Raster Image Processing: the processor inside the printer converts the data to be printed from whatever format it currently exists in, into a bitmap of the page to be printed - this is then stored in raster image memory. • Charging: An electrostatic charge is then projected onto a revolving photosensitive drum inside the printer.

• Writing: A laser beam is directed at a rotating polygonal mirror, which redirects the beam onto the photosensitive drum. The rasterized data in memory is now read, and used to control whether the laser is on or off, as the beam sweeps across the drum - where the laser beam strikes the drum the charge is reversed, creating a latent electrical image on the surface.

• Developing: The surface of the drum is then exposed to negatively charged particles of toner, which are attracted to the areas where the laser wrote the latent electrical image. The toner will be repelled by the negative charge on areas of the drum where the laser beam did not strike, and hence remove the charge. • Transferring: The drum is now rolled over paper, transferring the image from the drum to the paper (to aid in this process there is a positively charged roller behind the paper, which pulls the toner off the drum and onto the paper).

• Fusing: The paper is then passed through a fuser, where rollers provide heat and pressure to bond the toner to the paper. • Cleaning: An electrically uncharged blade and a discharge lamp remove any toner and all the charge remaining on the drum (this will all happen in one revolution of the drum).

Advantages of laser printers • High quality printouts – better than ink-jet or dotmatrix. • Fast printouts – faster than ink-jet or dot-matrix. • Prints very quietly – quieter than ink-jet or dotmatrix.

Disadvantages of laser printers • Most expensive printer type to buy, especially colour lasers. • Toner is more expensive than ink-jet cartridges • Expensive to repair – lots of complex equipment inside. • Fairly bulky – larger than ink-jet printers.

Laser Printers • Laser Printers are mostly used in offices or situations that require bulk, high quality output. • Laser Printer speed can vary widely and depends on many factors, including the graphic intensity of the job being processed. • The fastest colour laser printers can print over 30 pages per minute. • Laser printers are generally much more expensive than inkjet or dot matrix printers. A good laser printer would cost more than € 300, certain laser printers cost thousands of euros!

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